mamba max 6900 limitations

I'm kinda dumb and don't that much about electronics in general, but I have a question about running a 6900kv on 3s. What's the main limiting factor? I know you're not supposed to, is it mainly because the motor itself can't handle the rpm or is because the speed controller can't handle the load and generate too much heat? I've noticed the sidewinder 5700 says 2s limit, so I'm thinking its an ESC limit, because the same motor can do 3s on the max. And the 7700 with 3s will put it in dangerous rpm territory. But what about the 6900, its kind of an in betweener.
Warranty aside, the 6900 on 3s with a CC BEC does seem pretty stable and ballistically fast and the temps are surprisingly very low on the motor and within normal operating ranges on the esc. I have my punch control disabled and have taken steps to assure low operating temps.