I have gotten pretty accurate AF from my 85 F1.8, 35F2 and 50F1.4. I generally shoot at F2 with these lenses and smaller with the 85. Depth of field is pretty slim with the 85, even at F2.8 on my crop, and would be much less on a 6D.
I use the 35 mm focal length much more than the others, and have no difficulties with the old 35F2 lens wide open, even at night with mixed artificial room lighting. Here, F2.8 would not work for me. If photographing people, you need high enough shutter speeds, and the IS on my newer 35F2IS won't help. It does allow very slow shutter speeds when shooting objects, say 1/15 or 1/20 sec. I use center point focus and never recompose in low light...I crop afterwards.