did you already have the second card? it might work but for particular generation scaling is not so good anyway. and there is also issues with frame time. but most importantly AMD no longer support the 5k series in main driver. so for any upcoming games crossfire will not going to work because there is no CF profiles. of course you can still force CF to work from control panel but most often forcing CF to work this way is not guaranteed to work. and even if they work there might be graphical artifact.