265 -> 9.5", 275->10", you can run a 275 on a 9.5" but your cornering is going to be squishy as hell

 

you do not want stretch, 255 on a 10 inch wide wheel is more then a little stretch, and i agree with letsgetthisdone the evo needs a 275 tire for sure, this thing handles so much better its amazing,
i dont like the stretched look at all, to me the more meaty looking the better, obviously i wouldn't put a 275 on a 8.5 rim thats squishing the tire onto there, performance is gonna be compromised.

 

275 on a 9.5 is mint, cornering is not gonna be squish unless the tire you choose, (continental dws or dw ) they have super soft sidewalls. get a good performance tire with a nice sidewall and you steering response and feedback will be amazing,

 

255 on a 10" wheel is awesome, perfect amount of stretch for keeping the tire tight on the wheel without turning them into rubber bands

 

That miata has to be freaking awesome with those tires on it. I hope you are auto xing that thing.

 

More lapping days at local track, but I do autox once in a while too. Although I haven't done either yet on that wheel/tire setup. I got them after the season was over last year and weather hasn't been cooperating yet to start going this year... that and I got a couple things I need to do to the car before going back on track