@Clavulanic: I am running these stock with fan cooling only. I am expanding watercooling to all soon (the watercooled machine is 400MH/s per GPU and running around 60'C).  Stock (which mine are, except for 2x cards) are expected to be at 300Mh/s, so I do not understand why I should be way above 7.5GH/s.

If you have any suggestions on how to "fine tune" my operation - let me know. It is always easier to tell someone else to destroy their $800 card instead of your own :-)