I don't know, that group we had last night was kicking some serious Naxx ass. We have several 5k+ dps'ers (myself included), we might not be too far off.
Hard to say. Naxx dps is hard to gauge because a lot of it is inflated on aoe spam on large trash pulls.
Even on our 3D-25 runs, recount listed dps on Tenebron, where heroism uptime is nearly 100% and dps rotations should be single target, there are some people who still struggle to break the 3K plane. Granted, there is movement involved there due to lava waves and void zones, but the same would be expected if the dps were to shift to Sarth instead.