I am going with Georges on this one. The power will be Michaels, but GSP will have the speed. The difference for me and the biggest problem that Bisping will be facing is balancing his ability to commit to his striking, while constantly defending the takedown.
GSP has a pretty good read on Bisping, Mike is trying to goad St. Pierre into keeping this fight a war on the feet. Not going to work, Georges is the most calculated fighter in the history of MMA, and he has had four years to plan his comeback, the guy is not going to abandon his bread and butter that this point. If Mike is constantly defending the takedown, it is going to affect his ability to exchange. Look for Georges to mix in combinations, with takedown attempts. This strategy will keep Bisping on his back foot and will impede any offense the Brit hopes to string together.
A lot will depend on what GSP 2.0 looks like, especially after 4 years and 15lbs. But I really think GSP would have pulled the plug on his comeback if he was markedly slower or diminished. GSP 49-46, in a fight that will take place on the ground and standing.