In my opinion you want to try to get the drive shaft as close to straight as possible without going past straight under acceleration.. my old application was about right with 3*.. now I run 7*.. I bounce between bias and radials all the time.. and never change pinion angle.. maybe you can get a camera down there and watch what's going on and get an accurate set up for your combination

In the 8s N/A.with Brett miller W8's
5.07 at 133 at 2700lb