i run 15x6.5 MX-6 rims as my autoX setup, wrapped in 205/50/15 Azenis. to me, the main benefits are the lower rotational inertia that comes w/ smaller wheels, and the fact that the 15s are almost an inch shorter than my OE 16s, somewhat compensating for the car's meager power on course. i would love to move to 7" or even 7.5" wide wheels sometime.