Is it possible? Sure, my 280X is currently doing 4.83MH/s on X11.
EDIT: 4.9MH/s, now.
care to share your config?
"xintensity" : "64",
"worksize": "64",
"hamsi-expand-big" : "7",
"hamsi-short" : true,
"blake-compact" : true,
"keccak-unroll" : "8",
"luffa-parallel" : true,
"gpu-threads" : "2",
I worked off of yours, I'm pretty sure my X11 is in the ballpark of 35.20% faster. X13 around 38.51%, and X15 about 42.87%.
What about 280X?
EDIT: I cloned the develop branch of your repo - is this a joke? 4.55MH/s on X11 on my 290X, tops. It's at 1000/1500.
EDIT2: Though I am liking the xI 64 - getting 6.14MH/s almost on my 290X, 1000/1500.