If you can make weight for a weight class, you get to fight in it. If you want to fight in a higher weight class, that's your business. If you're not the guy fighting for a living stfu about what people "ought" to do.
On the question of how would he do I think he'd do well, and beat a lot of the best HW fighters. JDS is hard to call, as is Cain. But most of the top ten are just souls waiting to be claimed by him as far as I'm concerned. Werdum, Nog, Mir, Barnett won't be able to lay hands on him to drag him down (too slow). Overeem would die of cardiac arrest after 2 rounds of being circled. Terrible matchup for Nelson (Stipe II).
Stipe and Browne are the lowest-ranked HW I think could cause him trouble. Maybe Barry could hurt him bad with leg kicks if he managed to tag him.
But there's no need for him to move up, he has better competition at LHW essentially and can make the weight. And he's basically God etc.