Well, My wheels are +38 and I have camber adjusters, I run 195/50/15 tyres and the least camber i can get away with without fouling the arch's is around -2.7 degree's.
I had the camber set to 0 degrees today and if the arch hit wheel, it would have been a disaster lol.
It's all about the camber you want to run, if you want to run that setup with virtually no negative camber you need your arch's rolled.
In answer to your question.
I would say you would be safe upto +37 possibly +36 on an oem car slammed on coilovers without messing with camber, more if you have camber adjusters and want more camber to tuck a lower offset .
My front with +38 doesn't touch the arch liner's and i'm pretty low.