I just built my AMD A10-6800K few months back and added a XFX HD 7750 and it does crossfire. It does gives a little bit of an improvement, but don't expect leaps and bounds. Also running 16 gigs of Ram at 2133. Like the previous poster said, the APU uses some of the ram (about .5 to 1 in my case). So the more and faster the better.
Playing Diablo 3, POE, Firefall, GW 2 on close to max settings on all these games. Also do a bit of Autocad work and it works fine. I have not test it on more demanding games, but I don't think the APU will do too good on them. Overall pretty happy with purchase.