Now that you mention this... I have the same problem.
I always have taskmanager/speccy open up on another monitor so I can manage my temperatures and see if something is hogging resources and I've always noticed that my RAM would sit at 798MHz which was odd (I have a G750JW)
Upon downloading/installing CPU-Z, I've found that it is still 798MHZ.
I checked all around the BIOS but I couldn't find the XMP to change the frequency.