A note on using XMP mode.
I use XMP only to find the mfg fail safe settings of a given kit. I will enable it once to see those specs/timings to record them on paper for the purpose of setting them up manually in bios to eliminate timings and Vdimm settings as a possible reason for a failed overclock. I have found when overclocking to the limits of my hardware, for what ever reason, XMP fails where maunal setting have success. I'm not sure why this is but I know for example my current OC of 4.8 with all other settings the same except XMP engaged it fails with manual settings/timings it runs stable. As I have experienced this same anomaly with other builds I have come to the conclusion it's best not to use the XMP profile when pushing to extremes. Furthermore XMP is utterly useless when populating all 4 dimm slots on Sandy Bridge platforms because it always defaults to a lower than usable stable Vdimm. Not only is higher vccio/sa voltage needed to boost the IMC but typically in my experiences so too is a higher Vdimm requirement again when pushing to the upper limits of a proc. I don't believe this is exclusive to a specific motherboard, proc or memory kit as I have seen this happen with multiple builds. Of course YMMV just like some can hit a stable OC at substantially lower vcore than others with the same gear there are always variables in terms of what is achievable from one user to another but for me XMP works well when not pushing the limits, for that I recommend manual settings.
It is not my goal here to turn this in to a debate. It's one of those things that has to many variables to produce a clear winner, right or wrong. It is my humble opinion, so take from it what you will