Collins was a smarter boxer with more dimensions to his game, he was also tough and quite powerful and had good stamina. It'd be a hard fought battle but I'd favor Collins on points. Eubank was arguably the toughest SOB British boxing has ever seen, he also possessed not inconsiderable power, good stamina and conditioning, the shere bloody minded determination to keep fighting and trying to win until the final bell, and technically he was a better boxer than Froch. Again I'd favour Eubank to win on point in a war. Benn was ultra-aggressive, very powerful and very tough, but he did have some stamina issues and wasn't the smartest or the best technically. This I would give a 50/50 split should it go to points but if anyone was going to win via stoppage it would be Froch and it would be late.
Will I'm not comparing Froch to Kessler and Bute FFs! I'm comparing him to Benn Eubank and Collins! I bloody know Bute is 6'2"..... So what? Benn is 5' 9" at best Eubank is 5' 10" at best Collins is 5' 11" at best Froch is a great deal bigger than them. But not just bigger. Also he is strong and rough and tough....the worst kind of big! He is not just bigger in size but lets say a bit fragile...that kind of bigger guy they could cope with alright, but not Froch IMO.
I've heard that Froch only weighs a few pounds over the limit in the ring, fights at about 171, 173 maybe. That makes him a few pounds bigger than Benn maybe, who was 168 or 169 maybe. But Eubank was a genuine 180+ pounds in his super-middle fights, a lot heavier than Froch.
How many guys the size and level of the likes of Bute and Groves were Benn, Eubank, Collins even fighting, never mind knocking out? Their opponents were usually their own size, well under six feet, which is how things should be. That's the yardstick they should be judged against. Speculating how they would do against Froch is pure guesswork.