I fitted 17 inch wheels to my Puma - they were fine. You've got to use 40 series rubber - NOT 45's or they'll rub. Mine was lowered too by 30mm with Eibach springs from ESP design. I had no probs at all, but a mate of mine used 40mm PI springs with 17 inch alloys on his Puma and they kept bottoming- out.

Dont go with the Cossie alloys the off set means they will stick out of the arch.