I would not buy that 11" for Vitali Klitschko. Manny Steward, who wrapped Vitali's hands many times said they were among the biggest he wrapped with tape. Punching power has little to do with bicep measurement or fist size. But I do think the ability to make a tight fist, grip strength if you will matter a little.
Strange you don't really hear that many hard hitting heavyweights having hand problems unlike in the lower weights.
Genaro Hernandez had very bad hands. At 5'11" and 126 pounds there wasn't much meat on his bones, so to speak, so his knuckles were very prominent and they took a lot of damage. When I met Azumah Nelson I was struck by how delicate his hands were. That, to be fair, maybe have been because I was 10 inches taller and 60 pounds heavier.
Not without it's own set of drawbacks and the floating piece of bone in my right elbow can attest to that. Skulls are really, really hard.