My Boomkin regularly does about 1k DPS. He's been known to out-threat my prot pally if I'm not tring hard to tank. Without doing any severe number crunching, I'd say the big part is crit rate, crit rate, crit rate. Shaving 1/3 of his cast time off every time he crits does wonders for damage. The scary thing is, he's not that bad a tank. Yeah, he has no avoidance, but 12k HP unbuffed, 15k armor, and he can survive better than most anything else putting out that much DPS.