I had the opportunity to drive behind my car on (in my other car) on the way home from the track one day. Back then it had ~-0.5* on the rear (measured with a carpenter's square ,some simple math and a garage floor that is probably not flat) and it gained a notable amount of negative camber over bumps.
I know it has to do with ride height, as camber gain in increased as suspension compresses. There was about 1.5" from the top of the fender arch to my 17" wheel. And I had 10k springs on the rear.
I used it like that for 2 open track days before the turbo was installed, running 225 street crap tires. I didn't feel like it was low on rear grip, but instead it pushed like normal.
I don't drag race, but If I did (I would get a Mustang or Camaro
) I would try 0* and pretty tall ride height to minimize camber increase with suspension compression.
I run 0* on the rear now, and I've gained some traction while sliding, but it also feels like there's less normal grip back there for normal cornering.
Long, boring post. Don't read it.