I usually go as low as I can possibly go. It's not technically ATF, but I'm not physically capable of going any lower. The most I've done up to this point is 285 @ 175LBs, but that was after a few heavy reps and I almost did 2, so I'm sure I could do full squats with at least 300.
I don't do parallel at all though. It feels like it hurts my knees. Full squats don't bother me at all.