I would say size most defintitely matters. One of the guys at my class, is skinny, tall, and has the longest freaking arms I've seen in my life, like a freaking ape long ^_^ Another of the guys is huge, I mean like biceps the size of my thighs huge ^_^ Certain things work on bigger guys, certain things work on smaller guys. So yes, size makes a huge difference. One doesn't go the inside of a bigger guy unless you know exactly what the heck you're doing there. That's why I normally stay the outside, because I'm smaller than most. However, I don't think this pertains to who will win or not. The size and the strength that comes with it has to be applied through form. In my humble opinion, I'd say a small fast guy that knows a small fast guy form would be about even with a big strong guy that knows a big strong guy form, at the same training level. That may just be hope talking though ^_^