by just looking at his accomplishments id say kostya tszyu pulling a minor upset over mayweather would be my pick. kostya was big strong, he could punch very accurate and never tired. johnson unfortunately had too much bad luck in what would have been a close fight with calzaghe im sure getting the nod and i think roy jones was virtually invincible at light heavy in his prime, so much handspeed and footspeed even for a very good fighter like dariusz.
I don't see Jones-DM or Mayweather-Tszyu being that competitive, unlike Calzaghe-Johnson, which would be a fun fight, although one I would be confident in Calzaghe winning.
DM doesnt have any real shot against Jones. Calzaghe should have too much speed, movement and should school Johnson, but then again Johnson is technically better and may have had some of the success Hopkins and Reid had, combined with a good workrate to make it very close. Also Calzaghe was in the middle of a divorce, which distracted him from boxing Mayweather has the skill, defense and speed to outbox Tyszu for long periods, maybe the whole fight. Tyszu's defense is wide open, he is accurate though with underrated speed himself but doesn't press the action enough to land much, FMJ would find him a bit predictable. Tyszu's best shot is if he fights the version of Mayweather than fought Corley who probably wasnt yet strong at 140 and hurts him to the body early and keeps the pressure on. I dont really see Tyszu fighting this type of fight although he has a chance Probably Calzaghe or FMJ although I dont see either happening
I made a not so bold pick that Johnson would beat Joe when their fight was slated around that time. So i will go with that...Of course this was before he proved himself awesomely against Lacy and Kessler..When he was fighting 3 times in 2 years and having injury issues seemingly every second fight.
Johnson against Calzaghe. I see Calzaghe, Jones & Mayweather all winning tho (as most probably do I would think) I think FMJ & RJJ are just too fast as well as too good for Tszyu & DM, Tszyu v Floyd would be competitive all the way tho but the speed & extra class would tell IMO. Jones would beat DM clearly, likely wouldnt lose anymore than 3 or 4 rds if that. Johnson`s style would make Joe grit down & when Joe has to grit down, he takes a few himself but usually lands more himself & switches to boxing from the outside regularly enough to pull away, I feel thats what would happen here too. In order of upsets..... Johnson over JC Tszyu over FMJ DM over RJJ
This is very likely the correct answer in my perception, given Calzaghe is not proven at the weight in my opinion, i thought he lost to Hopkins. Johnson is vastly experienced at 175, though Calzaghe for me is better than him. For these reasons i don't feel we need to make a styles analysis. I rate Tszyu personally, and against Floyd looking to box him, i think he matches up very well, but the thing is, Floyd is so good at adapting when the situation is not great for him, that he might come out on top regardless.