Help Mixing & matching tires for an SRX250 ?

While searching for some tires in a hard to find size I am left with few if any options other than Bias-ply with great difficulty finding tires in the sizes I need, both from the same manufacturer & that are correct for rear & front use.
Any information on mixing & matching manufacturers, tread design, and other desperate acts such as using a tire intended for front use on the rear of a motorcycle ?

 

Stock tire size is
front 90/90/16
Rear 100/90/18

90/90/16 is nigh impossible to find in USA,
But per 2valve a 100/90/16 & 110/90/18 combo fits his srx.
This combo will have the speedometer read about 3% low (you will be going 3% FASTER than it reads.. i.e. at 100kmh you're actually going 103)

I have also calculated a combo of 100/80/16 & 110/80/18 will fit. This combo will have the speedo read .5% high (meaning at 100kmh you will be going .5kmh SLOWER/ you will really only be going 99.5kmh)
Both combinations come very close to stock & changes in overall gearing should be barely noticeable if at all (Speedo tolerances are often 8-10kmh off on my other yamahas so likely not exactly dead on target from the factory anyways)
The overall seat height would raise about 10mm with the 90 series profile setup. Seat height would lower about 2 mm from stock with the 80 series tires.
these other tire sizes open up MANY more tire choices & keep the overall Rake/level of the bike intact if used in conjunction with each other (don't mix an 80 series front with a 90 series rear unless you wish to have the rear 12mm higher than front etc.)

 

Good to know I'm overthinking it. I want cheap & easy, but not deadly either, already passed the easy point about 2 hours into tire shopping LOL.
I scoured all brand, tread & size options overthinking it all for way too long lastnight & heres what I found (& some answers for comments above)
i appreciate the input guys, bear with me here, not trying to be OCD on tires, just seeking a good safe semi frugal setup since stock is not an option here.
2 2valve, I know my "murica" bike is slow LOL no offense taken, its why i was asking what the carb secondary kicks in at before...which you kindly tested for me, no worries, i have plans to get it up to speed (84 xt250 cams i found nearby for $150, maybe i can prove/disprove the HP ratings discrepancies but yeah its slower than my bored jetted n piped xt225 as of now, i say its likely 17hp here, dont they know americans are often obese & travel long highway trips daily ? LOL, if anything japan with its 55mph limits & extreme population density should have been choked to 17hp !
I also feel speedo changes are negligible, even stock is often further off than these tire options would change, but posted the numbers for others as long as i had them figured. i had to post the math so others know just how close & pointless it is to figure out themselves
I did find i actually CAN get both your pirellis in USA !! Only in 90 series sizes tho (i was really hoping to go 80 series to stay closer to stock size, ride height, center of gravity, & also to have a touch lighter tire & less sidewall flex)
its looking like 90 series may be only way to get matching tires front & rear But concerning (to my newbie brain) the size you run on rear, is technically designed to be a FRONT tire !?!

Andych, yup theres a good chance I will be going pirelli route now i found em both stateside. Still hoping to find a true matching front/rear specific combo to keep handling as close to stock as i can (without sacrificing some grip or feel in the rear by running a "front" back there) but youre right, looks good/fits easy & most importantly AVAILABLE... it ticks all boxes but a front tire on rear.
I was alwaystoldg to go up 1" in rim size generally drop 10% profile, so your 17" sizes make sense. After i typed that lastnight later was thinking duh, i know how his dont rub, its not any larger overall than our 16s, its just less sidewall. I got 17" rims on a car that originally had 13", same idea. But that drastically changed the cars handling both for better & worse. thats partly why i may be overthinking this, tires change the feel of a machine more than any other part, i presume on a bike its even more pronounced ? run mismatch F/R on a car & cornering gets WEIRD etc. I do it on purpose in winter to "drift" a fwd car like its AWD & it works great !! snow tires up front + worn all seasons in the rear,but anyone else would crash in a heartbeat if not practiced LOL I assume those all magnify on 2 wheels so being cautious (if not pesky with too many questions LOL) so few choices I will likely end up like you say, it fits, its easy, good enough, but will always TRY to go for best I can at least.

DannoXYZ, I COULD run the stock size still in the rear, Its still available, but since front is NLA & must either go wider & taller 100/90 series, or wider & nearly same height 100/80, that leaves me with an imbalance front to rear for tread width and or profile. Excess grip or sidewall flex comparing one end to the other & then things get less predictable no ? (More an issue for a beginner) Could also affect the rake of the bike if not matching overall diameter if going 100/90 series front but a stock rear, but would be REALLY close to stock rake if i did 100/80 up front & stock in rear.
Its good to know as a racer you can get away with what i am reluctant to try as a newbie being all particular about tires, i can only imagine you put these tires to limits that will take me years to reach (if ever) & the ninja 250 is one reason many of these other size options are available, which is awesome, but dangit if it doesn't run a different size combo than our srx250 so i still cannot find a set of true one front/one rear tire matching tread in the sizes i want (except for battlax which is universal & have read a few bad reviews on them, they run on the high side for cost & most important, at my nieces birthday today my brother sa8d he's had them & echoed many complaints i read online) my brother also noted what you guys also have said, basically not a fast bike anyways, tires not a big concern even mismatched.

 

Ugh they got me, those marketing guys can sell ketchup popsicles to a nun in hades while shes wearing white gloves.

 

Thats awesome input ! Had I known the SRX already had a handling/grip imbalance & will slide out up front at the limit I would have been less persistent trying to stay balanced in changing tire size.
You mention raising the bike at all will increase trail, which I understand little to anything about (thinking trail is how far in front of the upper fork steering pivot the contact patch is ?)
kinda common sense an increase in diameter would raise the bike (or not at all if i go 100/80 series up front, which is why i have been trying to avoid the 100/90 series front which is taller than stock) but i never considered it would also push the contact patch forward a bit.
So in that case i will get a front tire in as close to stock DIAMETER as possible (100/80series 16 is closest) in an effort to keep trail same and be happy to upgrade the front 10mm wider to counter front end washout & not worry of a handling imbalance as it sounds to be an actual improvement vs stock.
I would prefer the bike is setup somewhat dumbed down for starters if only to make catching it easier for a beginner. I did a bit of a panic brake on my XT225 this summer at about 70kmh when a deer ran across road late one night. I must have STOOD on the rear because it did slide for a bit...yeah pretty scary when you dont expect it ! It caught again pretty easy.
. Honestly reminded me of intentionally leaving 40 ft white streaks of BMX bike rubber down the black asphalt hills by my house growing up, popped A LOT of rear tires the summer we discovered that trick LOL my xt225 is really light, kinda feels like a big mountain bike in many ways so it was an easy save to skid the rear at that speed. But i sure dont want front washout ! I tasted that once on wet grass on that same XT at maybe 20-30kph and it sucked ! Had to throw a foot down which is bad, lucky i didnt wreck it. But i'm still trying to discover where mine & the bikes limits give out. Would like to go sanely near them before getting bigger faster stuff.
Thanks for the input, i hope my ignorance is not seen as baligerence & please understand I will trust first hand real world experience such as yours over sales pitch hype etc.

 

So another vote for just ride it with whatever fits. Thanks for your input Murdo !
I live within an hour of Harley-Davidson, so vast majority of bikes I ever see, have drastically different front & rear tire shape, with the rear shape noticeably different. More wide & flat , vs skinny & round up the front.
Rather than using a big (&heavy) hog as my baseline, I will listen to what you guys say works. I guess I read too much into the front/rear tire sales pitch. I would've thought running two fronts would be about like running around in 2 left shoes or wearing your pants backwards LOL but if that setup never causes issues for anyone I am thrilled, as that makes finding tires a LOT easier

 

I did read up a bit on bias ply vs. Radial, which indicated radials took over somewhere in the early 80s as superior for sport bikes, it was racing that proved the radial advantage. So initially I sought radials for my new "urban sport bike" (& quickly found that was not going to happen !)
I would think even now the greatest force a modern tire will ever experience on a little 250cc will still be braking, or down shifting way too hard, the big forces not likely to be under power LOL, so in conclusion modern tire technology has advanced enough that a 250cc will be fine without being too particular.... Im so glad tire selection is no real worry, & am actually perfectly happy with "underpowered" stuff, have always had way more fun driving slow machines fast than fast machines slow, plus if you actually win theres that bonus of being the underdog hero
Still kinda feel funny running mobility scooter size tires, but boy are those scooter guys lucky to have access to such overkill rubber !!
Have learned a fair bit more about tires in the process so wanted to say thanks for helping me learn & discover along the way