http://www.ft86club.com/forums/showthread.php?t=38865
These guys know what's up. Look at the more popular tracks to see the well-tuned setups.
If you've thoroughly pushed the limits of a normal sized "street" tire like an RS3 or ZII, then the upgrade to 225 Hoosiers will be appreciated in dry conditions. Wider tires do give you more final grip, but there's a cost. To me, they feel a bit scrubby, numb, noisy, and under-utilized. Just my 2 cents.
I don't plan on being the fastest guy out there, but there's plenty of fun to be had with a light and simple setup like mine (215/45-17 Dunlop ZII's and 17x7 Enkei RPF1's). Whatever configuration lets you enjoy the experience.