For reference, this is a 6800 XT under water. I ran it just now with default MPT frequency settings. I just raised the power limit and GFX current, plus disabled deep sleep, then gave it 163v offset via EVC2 (total 1,313v). Clocks at 2800-2800 in OverclocknTool.
The point of buying a 6900 XTXH...