Killing Floor should not be a problem for the A8-6410. The below video shows it being played on a laptop with an Intel HD 4000. The Radeon R5 graphic core is a bit more powerful than the Intel HD 4000 so your results should be better; it's about as powerful as the Intel HD 4200.
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/www.youtube.com/watch?v=4UFlX-aPOno
Rome 2 is a different story... It is a real time strategy game which means performance is really dependent on the CPU. The video below shows many different games played on a core i5-3210m and the Intel HD 4000. Even though the A8-6410 APU has 4 cores it is less powerful overall compared to the dual core i5-3210m. Total War Rome 2 is at about 19:00 into the video (towards the end). It does not play very well. Kinda...