Any update on this one? AMD mining of Cryptonight is only "okay" -- basically around the same efficiency as a CPU in my experience. Still, given the poor performance of most other coins right now, it's something to look at.
it's also just okay on nVidia. It's because how the algorithm was designed (memory hard with plenty of random access)
A GTX 760 can rival an 8-core AMD FX CPU @4 GHz. So my Asus MARS rig (3 MARS ROG cards) is able to do 2.1-2.2 kHash