BoxRec

In a parallel universe, Peter manages to finish Wlad with a come-from-behind stoppage in that 10th round (where, I still think, if not for the bell - the ref would've found the reason to controversially jump in and stop the fight).

That fight was a double eliminator within IBF and WBO. So, Peter would've been in position to challenge either Byrd (IBF) or Brewster (WBO) in 2006. IIRC, Byrd had just cut ties with Don King at that time. Thus, King would've most likely moved Peter into a title shot vs Brewster (both Peter and Brewster were with King at that time).

Sorry for a long prelude. How would Peter perform against Byrd and Brewster in 2006?

I honestly think Peter would've won both fights.

Brewster-Peter would've been a shootout. And I think in 2006 Peter was fresher than Brewster. He could actually jab better than Brewster. And if I recall, he was a tad bigger. I believe, Peter would've eventually outfought Brewster after trading leather with him.

Byrd-Peter would've been a contrasting styles match-up. Boxer vs puncher. Byrd would've been able to frustrate Peter in portions of the fight and tattoo him with jabs and combos from the southpaw stance.

However, Byrd wasn't exactly a mover a-la Usyk. He often fought in the pocket, relying on his upper body-movement. And had a tendency to sit on the ropes.
Peter would've been unfazed by Chris's shots and sooner or later would've gotten to Byrd. Possibly, hurting him on the ropes and then - whatever happens.

At 2006 Peter would won both this fights.

2006 Peter could've and would've beaten 'em both.