It depends from car to car. With the 370, I think 3000 to 4000 (whatever you can get the rpm's to before the timer starts) and keep the throttle pressed exactly in the same position after the computer drops the clutch. RIGHT BEFORE you catch the rear wheels, very slowly increase increase the throttle pressure till you've pressed it all the way. The key is to get less revs than more.
Oh and if you don't jam on the brake, the wheels won't lock up. Usually right before I brake, I downshift. Do you know how to downshift-revmatch? That's the best way to not go under danger of locking up.