I have a different MoBo and different RAM. But I found that I wasn't able to use the XMP configurations reported by the RAM in the memory performance setting area of the BIOS. Essentially, I had to play around with it until it ran. Then I took a picture of that screen to memorialize the settings so I could put them back when something happened to them.
I was told by my RAM vendor, and from reading the Intel documents, that 1.65V was the max you should set. But if your system is running at 1.5V it's better to leave it there. Check with cpu-z to see if your RAM is really running at the clock rate you think it is. (CPU-Z shows the real clock that you have to double to get the effective bus speed.)
As you note, the default of 1333 seems reliable. Getting more was a challenge. I got mine up to the 1867 rate but I was unable to get the 2134 speed to be stable.
I'd suggest running some kind of memory test utility to walk across your RAM and test it all to see if you get any faults resulting from the 1.5V or other configuration settings. If you do, I'd slowly walk the V up and stick with the lowest setting that seems to work.