First off, I am a huge Joe Calzaghe fan, but in reading many of the posts, it is clear many of you haven't seen many of Marvin's fights, and certainly didn't see them in the context of their times.
The only time Marvin was knocked downwas against Roldan and it was a slip, with a punch sort of aiding to push Marvin down.
I one wants to argue that Marvin's big wins were only against smaller fighters moving up, it's partially because he cleaned out the division and fought everyone who mattered on the way up while every champ avoided him. He was probably already past his prime when he won the title.
His skills a boxer are also underrated here.
If one wants to argue the opposition Hagler fought, tke away an overrated Jeff Lacy, a faded Chris Eubank, and two fighters well past their primes who both dropped him, in Jones and Hopkins - especially when the Hopkins fight is one many feel he lost ( I thought Calzaghe won easly,) and the only big win left for Calzaghe is Kessler....and who has he beaten?

Personally, I think it's a great fight, and it could go either way. Marvin cut people with his rapier like jab though, and I could see thatbecoming an issue in the fight. The only time Marvin was ever cut to speak of was against Hearns following the headbutt. Once he had the title stolen from him in his first bout with Antuofermo, he resolved to not go to the judegs , for fear the title would be stolen from him again, and considering the scores after twelve against Duran (one of my favorite fighters) and the Leonard decision, he had reason to.
Marvin didn't move up in weight, partially because the move would have been all the way to Light-Heavyweight, as the Super Middleweight Division wasn't created until late in his title reign, or possibly, even after his retirement. That menat the only title to contend for during most of his reign was through Michael Spinks, and the numbers and interest compared with the other fighters moving up toward Hagler made them the far more lucrative and interesting fights.
I'd probably go for Marvin by either late TKO in a fifteen round fight, or by a close battering decision. Of course, Calzaghe's ability to adjust would make the fight very difficult, and her could pull it out.
I'd also pick Marvin in an easy but hard fought decision vs. Hopkins. He had too much power and a much better workrate than Hopkins; If you lay against the ropes vs. Marvin, you would pay, body and soul. Who ever was as good a fighter after they faced him as they were before? He punished you from the ouset until the fight's conclusion.
For the record Marvin was 5'9 1/2 inches, not, certainly a giant, but not exactly Jake Matlala either.