Comming from a combat training background (by combat I mean where complete incapacitation is the end point) if you train at 75% you will output 75%. At least every once in a while you have to go to 100% otherwise you will never know what that is! Having the capacity to do this without causing considerable bodily injury requires an awareness that takes a lifetime to develop. Otherwise you just need to have balls, luck and a stronger will to survive...
Realistically in order to be able to dish out the beatings you have to know what it means to get beat.