Im in 457 ilvl... not best geared and enchanted (not many time to play), geared for exp hardcap with a exp/armor elixirs (nice choice to smooth 5% extra physical dmg and reach the cap, they are so cheap, took like 100/100 from AH for 12g).
We killed 2 bosses and the damage taken by me was almost the same than a warrior much better geared. Healers "cant" tell acurate tips about how difficult we are to heal coz they were a bit starved of mana for raid... still my dmg was noticeable.
On par with the benefits of exp hard cap in the defensive side (steady chi and healing) we heave high dmg, in a low lvl raid gear for all raid members scenario we can help killing the boss. I was tanking stoneguard boss with 2 bosses moving arround and did 67K dmg... 2nd in dps to a Rogue with 77k and the rest near 60K, i think this is another thing to take into consideration, not to aim for, but its a colateral benefit of our tanking model and gearing.
If i have to say a downside of BM is the "last" portion of life we have, the "ohh shit buttons" are more tricky and we need to time our rotational cd to keep alive, pray you got 2 chi and guard off CD!!
P.D.: The symbiosis spell be get is a TOTAL CRAPPPPPP... it was said a 25% dmg reduction, Survival instincs symbiosis mode 25% down of 50% for 6 seconds, still was great... what happend to that??? ohhhhhhhhhhhhhhhh =(