madsmagnus :
Yeah if you are going for dual graphics then you have to use a GPU that is running GDDR3 > the R7 250 is the best match there.
But if you are just getting a GPU for max performance then I probably wouldn't be scared of throwing a R9-270 or 760 in there..
No. gddr3 gpus are generally a lot weaker than the gddr5 version. Plus it has nothing to do with CF.
The best gpu you can CF with the apu is a 7750.
You are better off disabling that though, and getting something like a gtx 750.