Re: if they were all at their peak.
That's just a lot to consider. I don't think anyone is going to just win against everyone. Certain fighters are going to lose the battle of styles. For example, I think Dos Santos beats Fedor, but I believe Cro Cop takes Dos Santos. Let me break these down quickly:
I believe Dos Santos can do to Fedor what Arlovski was doing, without getting walloped when going for a jump knee. I know, I know, Arlovski wasn't landing anything flush. 5 rounds of that would still lead to a lop sided decision if Fedor fails to land the knockout blow.
Dos Santos defeated a 35 year old version of Cro Cop. I believe a younger Filipovic reaction time would make a big difference. For some match-ups, I feel it is important to clarify whether it is in a ring or a cage for Cro Cop. I don't think Cro Cop performs well in the cage. I don't think it matters for this fight.