Every time some one says size matters in MMA, it always makes me think of UFC 3.
<iframe src="http://www.ebaumsworld.com/media/embed/854138" width="567" height="345" frameborder="0"></iframe>
Granted, the UFC is completely different now, but skills not size is the ultimate decider IMO. GSP probably would have the best skill set of all the fighters Silva has faced to this point.
et noli esse incredulus sed fidelis