In my case under windows this is not a problem, because I can just change my monitor to one of the 5870s I got on x1 extender, but under Linux that doesn't work. And no I can't really reorder my cards so that the 5870 is the one that is #1.
Not connecting a monitor probably works for Linux, but I kind of need my monitor! If you know how to change which card shows desktop or know how to make the OC work for the second core please help.
Sorry I can't help. It was a dedicated rig that ran Bamt or windows, never tried any other distros. My multipurpose rig only has 3 cards.