@Maz
I had no real trouble leveling 80-85 as mutilate in basically my old raid spec (i.e., no Deadly Momentum), but I never felt like I was really dominating anything. And I definitely had to watch out for adds, but I guess the non-faceroll was what Blizz was going for. For reference' sake, the rogue was in mostly ICC25 gear when he ventured into Mt Hyjal the first time.
As a point of comparison, I'm currently leveling my mage and pally (both L.82 now), both of whom were in i200 or lower WOLK gear. Haha, actually, the mage was head to toe in S2 (yes that's 2 as in two as in L.70 arena gear -- he was my first toon, but kinda skipped WOLK), now that I think about it. Anyhow, mage started off frost and really felt underpowered. In a way I was kinda enjoying actually having to nova/blink/kite a bit in order to finish off that last 1/3 of a mob's hp. Was strange at first, after WOLK, where everything died before it got to me, but after getting over that shock, not too shabby. Then I switched to arcane and it became a cakewalk. ABlast automatically applying Slow instantly makes arcane a super viable leveling spec.
I kept the pally specced prot just for esses and gees. Stuff dies kinda slow but I never have to worry about checking my hp bar like I did on the rogue. Overall efficiency I'd say is lower than the rogue unless I'm in a situation that I can pull multiple mobs and Hammer of the Righteous gets some use.
As people have mentioned, TB dailies are a different story b/c of how packed together they are and how quickly the mobs respawn. That said, between Combat Readiness, Dismantle, Evasion, Recup, Blind, and my personal favorite iwin button, Vanish (cuz if I'm not losin', I'm winnin', amirite?), we do okay.
At 85, it's hard for me to say whether mut is ok, pve dmg-wise. I'm only doing 5mans so far (heroics now), and mostly pugs at that. I generally am way ahead on recount, but see my prior sentence for why that's nigh irrelevant. The couple of times I haven't been on top, it has been a hunter with a better gearscore that beat me. Not sure if the luck of the draw has just grouped me with better hunters or if the hunter class is actually better.