On the one hand, melendez should steamroll Diego, however Diego's fighting style has led him to get favorable decisions in the past for some strange reason. DC should also annihilate Roy but at the same time we are talking about a HW fight and while DC might have a good chin, at HW, and fighting Roy Nelson one shot could put him away. Sudden KO's happen way more at HW than at LW and Nelson has been known to deliver them.
It's pretty much a toss up for me.