just trained front squat last night. i did a warmup heavy single that felt like it was near my actual max. i used 250 lbs. my back squat max is around 315.
i have tried both grips for front squat and have felt that the clean grip is more stable for me. it was more difficult for me to keep my elbows up with the cross-hands grip.
in terms of finger slippage, that hasn't affected my lifts. i start with 3 fingers on the bar, but since my index and middle fingers seem to be the main stabilizers, the ring fingers almost always slip off. sometimes i even start with just the 2 fingers anyway.
but i've found high elbows to be the most important point rather than the fingers. in fact, when i'm working with light weight, i sometimes don't use any fingers at all -- the bar just sits comfortably in the delt+pec groove when my elbows are high. when i'm able to do this -- i've only done it with around 135 lbs. -- it feels the most comfortable/natural, and i actually feel like my form is better.