5k is where most DPS should strive to be at, this is not unreasonable to meet so long as you're making the most of your abilities. High 4ks aren't bad either, but 5k is definitely what you should be trying to hit as a raider.

6K is going into optimization territory, and knowing the fight extremely well.

As for 7k-8k, 7K will depend on your raid comp, while 8k was probably fed buffs.