From a purely performance perspective I' probably go with the 996 turbo over a C2. If the choice were between the C2S, I'd probably go with the S. (Be weary of some of the early turbo's second gear syncro issues.) I would have to consider each scenario individually as there are so many options with Porsches.
Yes, the Metzger dry sump engine is more bullet-proof than the wet sump in the 997 Carreras but it's not like the na Carreras are exploding either. They have proven to be very, very reliable.
I would only consider a 2003 turbo or later as there were some visual and mechanical improvements with those model years.
With all said above, the OP must be aware that any 997 has a much better interior than the 996's. Visually, the exterior of the 997 is much more pleasing, imo. And, 996 turbos do not feel as precise as the 997 C2(S)'s. You know you are in an AWD car unlike the 997 turbo which feels very much like a RWD car. When I test drove my friend's 996 turbo, I felt that the car was not nearly as nimble or as precise as my 997 C2S; which I owned at the time.
I know these cars and the options very well. I have owned a 997 C2S, C4S, turbo and presently a GT3. If the OP wants any advice regarding specific cars, I'd be glad to help.
Last edited by devo; 01-02-2010 at 04:06 PM.