Judging by the recent press conference with Murray, Gennady's knuckles/fists seems to be huge. Maybe the reason of his punching power ? Liston's fists were huge too.
More than the hand size, its important the hardness of the hand bones. Many boxers had their potential handicapped when their hands started breaking. You cant hit full force with a broken hand. Or when it hurts even while not being broken. Unfortunately hand hardness cannot be valued from the outside, but given the savage punches 3g delivers on heaybags, it looks like his hands are tough.
apparently james toney had fragile girl like hands, or so said a poster who met him on here. GGG looks very robust, naturally heavy boned.
If you actually boxed and been to a boxing gym, you would know that hand size doesn't have that much of a significance in punching power. It's just a cliche that people that never boxed use.
Hand size has zero to do with power. It's all about his nearly perfect biomechanics, timing, accuracy, punch placement, and punching through, not at a target.
It obviously has to do with power, since a greater surface area ( and bigger bones) can whitstand stronger pressures. Guys with bigger hands can hit harder as they don't risk to break/damage their hands. Also, mass x acceleration effect means bigger impact.