It's been widely said, including by myself, that players in T5-T6 will not find upgrades before the late 80's and even Naxx.

Well, I was wrong.

I found my first good upgrade in Gundrak (level 75 instance in Zul'Drak) and then another one in the Halls of Stone (level 76 in the Storm Peaks). And these are not minor upgrades: the cloak dropped by the Maiden in HoS, which can be reached -- and therefore, farmed -- in 20mn, is better than Teron Gorefiend's cloak, which is one of the best melee cloaks in TBC.

I completely missed these upgrades because I didn't run many instances in the beta, so if you are 75 or above, you should start running instances more aggressively (the two Halls instances are absolutely gorgeous).