17x7.5 will be plenty. I always argue that smaller(16") wheels will be even better....less chance of bend, lower purchase price, better ride quality, generally less rolling mass, and also in greater circulation(less rare, you'll be able to find one if you destroy one). Less attention too. No need to attract would-be thieves...
Concerning traction, you'll find several sticky tires to fit a 17x7 or 17x7.5" wheel. Anything larger might be overkill(waste of money you could have spent towards lighter, stronger wheels/stickier tires).
My priority list for wheels:1st: will it fit?2nd: if it fits, is it strong enough?3rd: if 1 & 2 are true, does it help or hinder performance?(is it too heavy? am i thinking about response, or bling factor?)4th: if it fits, has proper load capacity, decreases rolling mass, what is the cost? If it performs to a high standard, cost should be a non-issue.
This isn't a cheap hobby, and it's always been my opinion that wheels/tires should be a high priority.
Absolutely 100% of all performance mods are transmitted to the road through your wheels and tires. Get the stickiest tire and the strongest/lightest wheels you can find. This is the price of admission, if you're an enthusiast.
http://rayswheels.co.jp/cgi-bi...=TE37