Just received my hexacore + 5870 today . . . booted fine and then I put my ATi 2600xt in the slot just above (where it was on my 2008 MP with the 4870) and it will boot, it will get past the Apple logo, but then it will go to the blue screen just before the user login appears and it will hang . . . indefinitely. Do I need to put it in another slot? Anyone have any idea why this doesn't work?