I get a solid 3.15 mh/s with my 6990, and another 550 kh/s with my i7 4771
On Win8, I'm using a very basic command line input to get those speeds. Also the 6990 is clocked at 880 and 1250 which is the factory OC. The more I tinkered, the worse my hash rates were... so in the end I just went...