I am impressed by the hasrates you all seem to get. None of my R9280Xs go higher than 710 (and they get very hot, above 90 all of them and as a result the speed is sometimes reduced as low as 550).
I guess it is basically a heat problem... But it would be nice to be able to get 750 out of every card, it would mor eor less an extra card for me.
i'm not suggesting it, but i just got an MSI 280x which hit 90 degrees very quick before any overclocking
so i said fuck it and took off the heatsink (breaking the warranty sticker) and my god was that thing poorly seated. giant gobs of thermal paste, very poorly spread. carefully put a thin coat of arctic silver and replaced the heat sink, now it runs around 710Kh/s at 70 degrees
i also have a powercolor card that runs at about 740kh/s without overheating, but curiosity got the best of me so i checked that one and it's thermal paste was as expected (only improved temp by a few degrees)