An R9 280X has been added to the hardware comparison page. With OpenGL, it's either as good as the original 7970s or better. At this point, it seems to be way better than the 7970s. It looks like whatever they changed has fixed the original 7970 issues.
https://litecoin.info/Mining_hardware_comparisonThat's pretty impress at I=13..Wonder what it does at I=18?...Maybe 800~900 kh/s....
I believe I=13 would be the highest point, some card just don't work well in high intensity.