GSP is a monster of an athlete and so is Alistair Overeem. He has the perfect look and is in perfect shape for a 260 lbs man.
I would defiantly back Overeem in an arm wrestle, but no seriously you have a valid point.
I watched this stupid charity event called sports relief they run over here in the UK years and years back, they got 10 of the UK's top sports personality's and athletes at the time to compete with each other in various endurance events to test there athleticism ability, the events where legit things like most swats in a minute, most shuttle runs, strength events etc.
The contestants induced guys who had competed and where currently at the time competing for us in the Olympics in all kinds of events including running, 3 Premiership footballers, Andy Cole and Dwight Yorke both playing for Man Utd at the time, Gianluca Vialli who was player and manager of Chelsea at the time, so as you can see they had seriousness athleticism individuals in this event.
Surprising thing was and why I remember this so vividly is that this event was completely dominated and I mean DOMINATED by a rugby union player called Austin Healey who literately smashed everyone in near every event, he won by a mile it was not even close, in distant second place out of the 10 contestants was another Rugby player who had just reached the end of his career and gone into retirement, none of the footballers even made top 5, it was a real eye opener for just how athletic the guys who play Rugby are.
My point been these Rugby players where both way bigger than any of the other contestants and smashed the competition, going on that evidence there is reason to believe the Reem would do the same to GSP.