You wouldn't want more than 2 degrees negative camber on a road car, because it will cook the inside edge of the front tyres unless you're cornering hard and often. 3 degrees on a track car (with tyres cut with a blade buff to suit) will give even tyre wear and plenty of grip, and the thing will be awesome fun, turning in beautifully and a joy to throttle steer.
BTW, I believe you meant positive castor ;) - negative castor is baaaad.
