well, that's the stock size tire for 2nd gens, as well as berettas, with 15s. it should be fine for your 3rd gen, too.
you can use
http://www.miata.net/garage/tirecalc.html as a good guide for tire sizing.
Have you seen the turbo wagon?
14.069 @ 98.91mph
229.1hp & 261.7ft/lbs @ 6psi
no tuning time
The FAQ has a great tire size to wheel size chart, check it out.
I may not be the sharpest crayon in the box, but at least I'm a pretty color
