I was pulling almost precisely 6k on northrend beasts yesterday in a 25 man pug, on the first mob of the northrend beasts encounter. My gear is in my sig, not really amazing but decent enough. I guess if you had mostly ilevel 245 or 258 gear and the T9 set bonuses, 8k dps on a standard fight wouldn't be too hard to hit.
I kinda hate dpsing many fights in ToC and Ulduar because there is far too much target switching, and Corruption falls off a lot. The magnataur is fine, but every time the jormungar burrow i have to ramp up 5 stacks again. It also happens when icehowl knocks everyone against the arena wall. Really irritating to be doing 15 seconds of substandard dps while getting back to a full stack. Ditto on jaraxxus when the adds spawn. And rets do awful dps on faction champs, because divine storm and consecrate do 25% normal damage and are too risky to use anyway. Twins also forces you to switch, and anub burrows regularly too.
XT-002 always annoyed me cause i'd be neck and neck with the combat rogue in the guild, then the heart spawns. So while i'm stacking corruption on it, he's blowing Ad. rush and blade flurry and jumping to 10k dps. Koralon makes up for it though, since it's eeasy to tab target and keep a full stack on him and both arms :P
I'd prefer Corruption to be a self buff that stacks when you attack any enemy, unfortunately that would be too powerful in pvp.