you won't need to try and turn a 996 into a S4R, it is really close to one as is! there really is very little between them, the 996 is geared taller, the S4R has shorter duration cams (st4s). for city hooning, oops, sorry, riding, the S4R is way better than a 996, for track days the 996 is better. where will most of the riding be done? from your post it looks like you are thinking of a new S4R, if that is so, i'd buy a new bike over a 2nd hand 996 every time. knowing the history,getting a warranty, not to mention the free service deals going! a good 996 is a nice bike for sure, but i love my S4R and it does everything i want, including track days.