yeah, this fight already happened, and bj kicked his ass. that was back when he didn't train too.
penn is just better everywhere. on the feet there's no comparison, and serra's best weapon, his groundgame, albeit good and pretty aggressive, is nowhere near penn's. it's funny that penn has become almost an exclusively standup fighter as of late, because he was the world bjj mundial champion after only three years of training, and that's why he debuted his mma career in the UFC.