I drove last year with dedicated snow tires, the ones recommended by Porsche, on my 18" wheels. There was a bit of snow, lots of ice last season in Tulsa, Oklahoma, and I had no trouble whatsoever. I don't have traction control, but it really wasn't an issue.

I recommend using the Porsche recommended snow tires when the temperature drops below 40F and enjoy your car all year long!

 

Oops forgot to mention my car is a C2.

 

I'm impressed with all the C2 owners driving their cars through winter.
Living on Canada's East Coast I figure I have to buy a C4(S) if I want to drive the car all year round, but the response so far seems I might get away with getting a C2...Anyway, one other potential problems for myself is that I have very short, but steep driveway (sadly not heated) and my question is how easy would a C2 on snowtires get up on it when it's icy/snow covered (starting from a standstill)?
Even with a front wheel drive car (on all seasons mind you) it sometimes gets a bit tricky.
Any input greatly appreciated,
Cheers
KK