Prior to Bowe becoming fat, lazy and clearly unmotivated he had the size and skill to give any HW of any era a good fight. His biggest problem was not using his size and being drug into a slugfests when he could use his height/size and jab to stay out of trouble. So for arguments sake I think we are calling Bowe's prime around the same time he beat Holy in their first fight (1990-92)

Tier 1 opponents:
Lennox Lewis - I think Bowe's size and skill would give Lennox problems but the patient Lewis that Manny made would have fought smart and avoided mixing it up. Winning either with a late stoppage or UD. Interesting that these two's prime was so far apart.
Vitali Klitschko - Bowe would have been drug into a slugfest and I am betting on Vlad being the stronger puncher and tougher of the two. Mid round KO for Vitali
Wladimir Klitschko - I think Bowe wins this with a late KO. Wlad is chinny and Bowe had the size and talent to hit him hard and often.
Chris Byrd - 1991 Bowe KO's Chris Byrd ala Ike style
James Toney - Tough call and I am not sure when Toney's HW prime is, but I think Bowe from 1991 could out work Toney and win an uneventful UD/SD
John Ruiz - I don't think Ruiz would be able to wrestle a SD away from a fit and motivated 91 Bowe. Bowe late round stoppage.
Tier 2 opponents:
Mike Tyson - I'm calling this a push. If Tyson couldn't overwhelm in the first 6 I think Bowe's size and jab would end the fight in the championship rounds. Hard to say if a 1991 Bowe had the experience to weather a bull-rushing Mike.
Lamon Brewster - Bowe by KO inside of 5 rounds
David Tua - This is either Bowe by a boring UD or Tua with a 12 round KO after losing every round
Hasim Rahman - Bowe by KO and it wouldn't be close
Jameel McCline - See Rahman
Sam Peter - Bowe by UD. Peter is too limited to beat a big talented heavy like 91' Bowe
Michael Grant - Bowe by crushing KO in round 5.

Tier 3 opponents: Bowe by KO for all of them.
Oliver McCall -
Fres Oquendo -
Kirk Johnson -