Good lipo cell can go as low as 2.7v, but I wouldn't routinely push any lipo that low. I use 6.2-6.4v as a cutoff depending on what I'm running. I want a little safety margin and won't miss a few min of run time anyway.

Just look for puffing (swelling) - as long as you don't see any, you're prob good. When I hit lvc, mine will stutter 1st, then if I don't quit, it will completely shut down, but I'm not running the same one.