First, I'd only try to use memory that is on the QVL for my board (regardless of speed). This just makes life easier.
While it was possible to use faster memory down clocked to a slower speed previously, I've seen less and less tolerance for this with newer chipset, BIOS, CPU combinations.
If it were me and I was going to invest in a board with a non "k" CPU, I'd go with the slower standard (matched) memory. This is not to say that faster memory won't work, but the chance for compatibility and success is lower. I want to "build, install, use". I don't have the time to tinker with these things like I once did. Plus for the investment, we all just want a system that works.