I was building a new rig and my 7950 sapphire 7950 boost oc works fine (only 16MH/s wtf) when i use the x16 pci-e but it shows as a hd 8400 when using a riser. It even says it has 1.5gb of ram instead of 3gb. claymore miner couldnt create the dag. tried it on 15.12 and the lastest drivers too but couldnt get it to work. (fresh windows install too). The riser works with a 270x perfectly.