I think the best one you can pair with that is an R7 250 DDR3 (has to be DDR3, shares RAM with system). Dual graphics isn't really worth it IMO, but the drivers are slowly getting better. At this current point in time you are better off getting a 7770 or better. A little bit more money ($10-20 maybe), but way more performance.
APUs are meant for a single chip solution and lite GPU accelerated programs. If you want gaming performance, an APU wasn't the best way to go.