mmininginc - I have the ASUS R9 280x DC2 and 100% happy with it.
Like claygraffix I get 750kH/s with it. (undervoltaged + increased the engine clock with 80MHz)
But what I really like about this card is its superb and silent cooling system.
745khs out of the box on stock. Voltage is unlocked so you Undervolt to save power and heat which lowers fan noise as well.
My ASUS 280X-DC2T is running at 800 KH/s each while undervolted to 1100 mV (stock is 1200 mV). I paid extra for the "top edition" model. Would be interesting to see what others get with standard model.
How did you undervolt these cards? I can't get the voltage to change. Running BAMT. Tried AMDOverdriveCtrl and atitweak. Atitweak says the card is supposedly at 1.1V as does cgminer's debug_oc when starting the miner but they are always at stock when mining.
I'm having the same issue....