I am not much of a raider and never did extensive tests when it comes to boss fights so I can't take a stand on PVE.
Pvp is much more reactionary and there are many more variables and the fights are short. I would go with T4 mainhand and crafted T3 offhand for the Bel's proc alone. Even post nerf Bel's too good to pass up and it stacks with Precise Strikes feat.