I just ordered these:
18x8.5 SSR GT10 BSPL Front
18x9.5 SSR GT10 BSPL Rear
They will have Continental ContiWinterContact TS810 S
Front: 235/40VR18 N0
Rear: 265/40VR18 N0
They are from tirerack.com. I
did order Porsche center caps as well.
Man, it wasn't cheap, but they will definitely fit an '05 and there weren't many that would, as far as I could definitely find out. I had found several that "may well fit" and if not "just send them back" and I'm not willing to do that. It's snowed here several times already near here and I need to drive in the snow.
As far as 17" wheels, all I could find were the "turbo look" wheels, not to my liking but considerably less expensive.
Go to 19" and there are no Winter tires, but several Summer ones, but I don't really want 19's, as my beat to hell back can use a little cushioning that 19's just don't have!
Hope this helps!