How much will I be gimping myself if I choose to go Beast Mastery at 85?
I've been reading about the different specs (stats, rotation, glyphs). I've even tried all 3 of them, and found that I prefer BM over the other 2. I know survival is currently the best DPS spec, but how much lower is BM? Is it still a viable spec to do heroics/raids with?
BM is not bad DPS at all, it's still very much competitive with other classes. BM pretty much lacks any decent AoE damage output, but thats not something you should worry about anyway really.
I believe both BM and MM are getting buffed very soon, kill command, chimera shot, aimed shot and kill shot all getting damage increases. So kill command is going to hit like a train. I play BM in pve still as I find it more enjoyable than SV, plus you can bring heroism to dungeons with you as BM, which can come in handy.
Basically, you will do fine dps as BM, and with the upcoming buff it may even be on par with SV dps.
You will pretty much be below an SV Hunter in many cases. Remember that regardless of buffs or debuffs to specs, BM is definitively a Utility spec now, so if you can manage to dismiss and pop a tank pet out to hold a boss for that extra second needed to kill them, you will be the hero of the raid regardless of dps.
BM will probably get a small buff soon, or SV will get a nerf, either way i think BM will be on par with the other specs in not to long, so if you enjoy the play style i think you should just hang in there for a little while longer