900 was simply too much for my card even with the maximum voltage at stock bios of 1.0870. The temperatures were well within acceptable levels to boot, don't think the fan even hit 60% come to think of it! It just black screened and the graphics card reset to stock levels whilst testing FurMark. Anyways been playing at 890 core now for a couple of hours and everything is rock solid. Let me know how far you manage to push yours.