one guy got
 above 5.7MH/s stable with my 280X on X11, using a kernel I heavily modified.
290X is getting 6.5MH/s at (almost) stock clocks, that is, 1000/1500.
7950 pulling around 4.87MH/s at 1120/1500.
And 270X getting 3.53MH/s at 1150/1500.

https://bitcointalk.org/index.php?topic=623409.1560

who knows to get it?