Im running 200k front, center locked, and 50k in rear. Im also parking lot racing on a medium grip track similar to what you described. I duplicated Paolo's most recent nitro GT setup and the car hooks and handles like crazy. Very happy with it at the moment. I tried lots of different weights on the center but never liked it. Locking it made a huge difference. Not sure if anyone else has experimented with it but it works for me.