Steve,
Das Sport makes the best pure bolt-in which requires no drilling and can be installed or removed in 1/2 hour. They run $800-900 verus $300+ for a standard bolt-in.
I run my cab with NASA HPDE and PCA DE's and find it very enjoyable. You can invest and enhance the performance just like any 911, though I wouldn't intent for it to be a full on race car. I've got 22/30 t-bars, Bilstein Sports, triangulated strut brace, and some chassis stiffining bars along the door sills. I'm as fast as any similarly equipped 911.
944/951's are nice fun competitive cars, but they just don't do it for me. Some day I'll strip the aftermarket stuff, turn the cab back into a weekender and buy a real track car. Racing is an extremely expensive proposition and right now it's not for me. Good luck.
John