That would be a fun fight to watch. One good leg kick from Barry could end it. GSP is much faster though, so he could potentially stay on the outside and out-point him. Could GSP take Barry down? That would be tough considering the size difference, but I wouldn't put it past GSP. I guess I would bet on Barry, simply because he would just need one good punch or kick to win, while GSP would have to avoid him for the entire fight and/or get takedowns to win.