Imagine they changed the rules tomorrow and made boxing 20 rounds..or even 6?

Obviously, a fighter would have to make adjustments to their styles in each case but the 20 rounders would be a physical attribute not all boxers would achieve.

Stamina must be one of the factors in a 20 round fight and also in a 6 round fight if your exerting more energy trying to knock each other out quicker.

For my 20 round fighter (i will give mayweather a rest this time) and go for calzaghe. As much as he annoys me for ducking a few fighters (imho)
i cant ignore his duracell battery fighting stamina and boxing skills.

For my 6 rounder there are loads of oldies to choose from and current fighters but i got to go with tyson.
He was built for 6 rounds with such great head movement with pendulam power shots its a beautiful thing.

Who would be the best fighters at 20 rounds and the best at 6 rounds?

Please give one answer for each and explain your choice..

Thanks.