Hi Ferris
So a single card pulls about 120 watt given that the MB swallows around 100W (Asrock 970 + Sempron 245).
If you could push the card higher than 400 kh/s it would actually outperform the R9 280X for 710-720kh/s.
As real world experience mentions that the 2GB card can reach 450kh/s, I would believe without any theoretical mumbling that the 4GB at least could perform the same and then some.
My mining rig consumes 800W (undervolted) with 3xR9 280X incl. MB consumption at 100W. That is around 0.38 W/KH/S for 700kh/s/card
If you have 3 cards you would consume 450W => 450/0.38 = 1184 / 3 = 394kh/s anything higher is pure win

Nice indeed
