I ran a 7870k black edition (CPU OC at 4.4GHz at about 1.45V and GPU at about 950MHz, Seemed to be running really hot but I think we had a faulty cooler (CM Seidon 120) ) in dual graphics mode with an R7 260X (2GB Gigabyte edition, GPU at 1200MHz). We were using corsair XMS3 (rated 1333, but running at 1600MHz with a little tinkering).
Machine was prime and valley stable for 6 hours - overall running dual graphics mode over just using the R7 260X on it's own made little to no difference for synthetic benchmark scores.
I built this machine with a friend for another friend who isnt too PC savvy. My friend built it, and I overclocked it and did all the stability testing.
This is more or less what we found:-
7870k using onboard graphics only - Unable to run valley benchmark at higher than low settings without considerable stuttering, CPU got insanely hot (touching 85C). only getting 20-30FPS in BF4 at 1080p, and only 40-50FPS at most in rome total war 2, spiking to 55 but dropping as low at 10.
7870k dual graphics mode with GB R7 260X - Able to push 40FPS in valley on high settings with MSAA turned off, CPU temperatures much more sensible (topping out around 75C). good playable framerates in TW2 and BF4 (around 45-55, dropping to 30 on occasion).
7870k with onboard GPU disabled - very similar to the above (45-55 FPS in game, valley 40 FPS on high with no MSAA) but CPU temperatures much lower (topping out 65C) .
all in all, we should have bought an FX chip and just used the R7 standalone. You can pick up the FX-8350 for about the same price as the A10-7870k, and IMO it's much better as a CPU, throw in as good a GPU as you can afford and away you go.
TL;DR even the most expensive A10 APU failed to impress me at 1080p, better off with a dedicated CPU and a dedicated GPU. OP if you can give us a budget I'm sure we can throw something together for whatever price range you might fit in