My GTS not only has locking rear dif, it is electronic, called PSD and uses accelerometers for car direction, speed, and amount of steering input to decide how much lock up is needed. Oh and there is the passive rear steering on the 928.
I've read that book and others too. In fact, I have taught a performan driving class at the local PCA autcross events.
Aero doesn't much come into play at the speeds of a typical autocross course unless you have those huge silly aero you see on some of the Japanese racers...
