DPS numbers are dependant on a lot of things - most notably the fights themselves. Remember that some of the earlier fights like Magmaw and Halfus have +damage modifiers on them, so it's perfectly feasible for someone with worse gear to put out huge numbers on them.
Some fights are also well tuned to different specs and classes. I barely know anything about Arms and only have a slight idea about Fury, so I can't really relate it to your situation but it's definitely something to keep in mind.
There's also raid buffs/group comp, and a lot of other things that go into it. I would never draw a line in the sand and say "well X item level should be putting out X damage!"