Back in the ICC days I was the in the top 5 PvE locks on my server, at least horde side. That was the end of my time raiding though. I kept to a small guild though, but I out geared basically everyone. Problem with the small guild was that when Cata dropped I leveled up so quickly that I just sat around waiting. And I mean leveled up super quickly. I was on pace to be US first 85 by a lot till I decided to sleep. Ultimately it took me just 17 hours in total to do it, and definitely could have done it continuously but I decided to go to class (college right, how dare they have classes) then the fatigue kicked in. But I was 75% of the way through level 83 just something like ten hours into the expansion.
So yeah. Two days in and I was 85. And my guild took weeks. I really blame that for my quitting the game. Randos could not handle the cc aspect of the heroics so LFG was pointless and the queues were STUPID long. And my guild couldn't get to a high enough level to do them quickly enough. I think I quit cata after a month and a half and only like... seven of my guild was at 85.