If you're running neoscrypt, each GPU should be at 320+ kh/s.
320k is maxxed for the 280x's, but the 290/290x are bottle-necked at about the same speed. There's an update coming soon to kick the 290/290x up a bit further.
Yeah that's NeoScrypt.
Do you have decent enough config to bring my 280x's to 320kh/s+?