I was looking at 997 C4S before going with the GS. They are pretty much equal in a straight line, but on a track the Porsche will do the quicker lap. It really is an everyday car, it is so useable, even in the winter. That was one of the things that put me off. I us my car as a weekend toy, so it still feels special.
One of my friends did go for the C4S, and has used it everyday. He admits it doesn't feel as special as when he bought it, and now I've stuck Larini's on mine he's decided he needs something a bit louder. That said, he bought it 3 years ago for 33k, and is about to put it back up for sale at 32k. So 3 years of motoring (everyday) for 1k - not to be sniffed at.