For the last few toons I leveled up, I turned xp off at 77 and ran them through cata dungeons. They were so op I just played them 1 at a time. In one AV I had over 200 killing blows. The blue gear blows away even the cata green, so that you one or two shot everything. My mage was critting around 30k.
Very Fun, but keeping xp off was a no go, there just weren't any queues.