Pro-Kits will take care of the "majority" of the wheel well gap and performance is gonna still be there. I would probably go with Intrax or H&R if I had 17's though. 1.7" drop as opposed to the 1.3"/1.2" you'll get with Pro-kits.
As far as 18's and Pro Kits go I think it looks good but I agree it does look a lot better with a lower drop.