May as well add my 2¢... Keep the thread alive! ;)
KJ is a f'ing pain, but
here's last night's wipe-fest report showing how close Mutilate and Combat (and 10/8/43!) are at about the same iLevel gearing.
The fight is tricky for Mutilate because of the need to collapse so often in the later phases which often happens while trying to refresh a timer and avoiding meteors and fire blooms along the way, harumph. So SnD occasionally drops and Rupture uptime is lessened because of the fight mechanics. The same can be said about Combat cycles, but refreshing those aren't quite as damaging to output.
Also of note: I'm getting an avg. 2237 DPS on this boss, but Mutilate is still generally weaker on trash from what I can tell. I'm often hitting Evis rather than Envenom as trash tends to die too fast to build enough DP stacks to make it worth it. Combat and HaT are better there. Also, I'm seeing the initial threat curve being smoothed out significantly by starting with only 1 HfB stack and building to 3 as it needs to be refreshed rather than starting with a full stack. This is more important with a Lock tank or situations where the tank is slow on threat for some reason. Just wanted to note it.
All in all, Blizz delivered on their promise for us in 3.0: Rogues have 2 viable raiding builds and not having a Retadin makes Mutilate even more useful to the raid. And most shockingly, a third spec is working as well for the time being. Several people I'm talking to are expecting HaT to be changed before Naxx raiding, so I'm not getting too excited about it. But all reports are it's pretty damn fun (CP generation is sick).
Anyone else have some data to share?