try this link here...
www.miata.net/garage/tirecalc.html
you enter in your old tire size and the tire size you want and it gives all diff kind of info back even how it will affect you speedo reading. Manifest, my tires are 205 50 16 which means your tires diameter is .7 inch bigger than mine, so we must have the same struts. im lucky that mine dont rub (just) thou.
Madrox, if your car is black then i would recommend the AME XR5 the same (or similar to the red GT) but i think they only suit black cars. other than that i personally like really spidery rims with large diameter and 5 or 6 slim spokes with a small hub. ive seen some with a matt black finish on parts of the hub to make it look even smaller which is quite a nice effect. hope ive been helfpful
p.s my standard wheels were 195 60 15 so the rolling diameter between standard and what i have now is almost identical, so the struts are nearly rubbing even as standard