Agreed its all on feel and lap time. I try to sense turn in to review front camber (also front ARB) . I find it quite easy to sense in game. For rear camber I monitor a) mid corner grip (any increase in oversteer when testing a change to rear camber indicating lack of rear grip) and b) Traction / accelleration out of corners. Lack thereof indicating too much rear camber. There is of course a tradeoff in these second two values (a and b). More rear camber will give you better mid corner grip but less accelleration. Its only your lap time that will tell you which trade off is netting you more time than the other is losing. But as an example at Spa with a higher number of fast corners a little more rear camber works well, at Monaco with constant need to accellerate from slow corners a little less rear camber seems to work.