Further details after more tests, this could be useful if you choose this card (even with the issue, I definitely recommend it!).
You cannot independently set 2D and 3D memory clocks on this card, but you can still use a workaround: AMD does not allow a memory clock more than 150MHz lower than the core clock. So, 750core/600mem is ok, 860/600 is not (and the memory clock automatically goes to stock 1200MHz).
You can create the following 3 presets in CCC:
- Stock: 860/1200 -> in 2D becomes 300/1200, in 3D becomes 860/1200; no flicker but idle power is high!
- Low Power: 750/600 -> in 2D becomes 300/600, in 3D becomes 750/600; there's a 20% penalty in 3D but idle power is 10W lower with no flicker (3DMark11 goes from 6426 to 5121 on my system).
- Auto: 860/600 -> in 2D becomes 300/600, in 3D becomes 860/1200; no penalty but there's flicker on memory clock switch
Hope that's useful for whoever wants to buy this card.