And the performance lost would be larger in more memory intensive tasks.
Moreover, how many users will be overclocking the FX chip @ 4.8 but underclocking the ram? Memory @ 2133 seems a more adequate timing and then differences would be a bit larger.
As you say, the APUs are much more sensitive to memory bandwidth. I read reports where the gain in performance is of up to 20% by using faster memory under windows. I know AMD chips usually run faster under linux. That is why I asked about what memory is being used in phoronix tests. This is important info (at least for me) which is lacking.
So far as I know AMD mobos support XMP via emulation. Enthusiasts users say me that the best results are obtained with AMD optimized RAM. I do not know more about this issue, and this is why asked to test some AMP profile.