With the front squat I’d guess not too much? My hunch is that my abdomen would fold if I went too much heavier. It’s a good question but not something I’d want to injure myself trying. The real difficulty in high rep front squats is the breathing. To do them your form has to be good and consistent or it just doesn’t work.
Front squats are a different game, even more so for high reps.
Doing 315+ is very impressive, just being able to balance the bar on your front shoulder girdle is a challenge. It's hard to breathe too.
I haven't done them with over 275 pounds in years.
But once you master front squats, they are amazing for growth and strength.
You don't see many people doing them anymore, because they are so difficult.
People loading up the leg press thinking that's how you get strong legs.