If it were me, I'd use a dremel to nibble at the heatsink a bit to make it fit. I wouldn't want to run a 4890 2GB on a x8, it just seems wrong. Like putting skateboard wheels on a monster truck.
Originally Posted by mr. biggums
its fine in the 8x slot, but if it bothers you just make sure your ram is at stock and you can take off the heat syncs.