Weight matters, but skill matters more. I outweight Pac by about 50lbs and I would expect he would beat me within the first minute of any boxing match. GSP I know is an athlete and has taken boxing lessons, but most professional boxers, especially of the calibre of Pac have been boxing for 15-20 years..and that's all they do is focus on that one sport. So if GSP holds his hands low, he's going to get hit, if he leaves his body open he's going to get hit, if he throws something slow, he's going to get countered, and on and on it goes. And if you give Pac 4 oz gloves, he's going to lay a beating on GSP in a boxing match..I'd bet money on that.