If you are honestly looking for something that can drag, track and be streetable; immediately forget the S54. It is inherently too slow, the supercharged ones are a waste of money and the turbo ones aren't worth the money. The n54 is great but I would not use it on a road course... too much can go wrong and the engine inherently has cooling problems. Even though it looks more expensive; the S65 appears to be the proper option for you. You really don't need a 15K supercharger to make the car run well...

Or buy an EVO9 and resolve all the issues at once.