One of my 5850s went out so I purchased a 280x since it is faster than my previous crossfire config. I still want to use my other 5850 for feathercoin mining. Everything works fine when the 280x is in the primary slot but if gets way too hot. I tries switching them but now my PC doesn't even show the 280x i n device manager.
I currently have the Asus 280x DCII card and it runs fine, but one of my friends is selling a EVA 680 4gb classified card for a great price. It also turns out that I'm building a gaming pc for another friend, so I may sell him the 280x in his build if the 680 is a worthwhile upgrade.