I've run my A10-6800K on 1333MHz, 1600MHz, 1866MHz and 2133MHz with satisfactory results on the last 2 specs.
The APU's built in GPU memory is shared with your system memory and the way it operates, it seems to like 1866 and 2133(sometimes higher) frequencies. The key numbers here are the frequencies and not the internal timings.
For the sake of reference, you could populate the dimms with DDR3-2133MHz @ C15 as well same frequencies @ C9 and yet not be able to tell the difference between the two.
However since we are talking about a FM2+ or FM2 mobo we have to assume that all boards of this socket will not allow you to change memory timings but only frequencies. Most of the reviews show the use of 1600MHz kits when using an APU system with a dedicated GPU but honestly that sort of practice would be...impractical since you would net better results gaming wise if you moved towards;
Intel G3258+H81 board+DDR3(8/16GB)1600MHz(with tight timings) kit and see better results than the APU route.