Direct from AMD:
I really can't say any more than that....
The display connectivity hasn't changed from the HD 5000-series as many cards are using the same traces, etc as the HD 5000 series. RAMDACs are the same as well.
Plus I just tried running a 2560 x 1600 display off the #2 (supposedly) DVI-I connector on a HD 6970....it worked.
All I am saying is that the layout may be different but if you are using the reference design from each generation, nothing should have changed. Non-reference cards though....your guess is as good as mine....