17 or 18 rims on my Gs-t?

hey guys i wanted to improve my traction and give my car some looks so i was looking into some rims. ive already installed a flex tein coilover system and the edfc so now its time for the rims and lsd. but anyways i wanted advice on whether to get 18 or 17 and how wide should i go 8, 8.5, 9????? 9.5?!?!??! tanx DSM geniouses appreciate the help once agian.

17's with larger sidewalls are most likely better from a racing standpoint. however 18's look a lot better in the 'fill the wells' standpoint. remember they will also be heavier and have less sidewall.