MSI Z97 Gaming 5 - no boot with XMP enabled

[pr0phet]

Hi everyone - first time on the G.Skill forums. Hoping to get some help. I just did a rebuild (components listed below). The mem is running at the Intel default 1600mhz - every time I enable XMP in BIOS or force the 2666 manually, I get a message that the overclock failed and the PC doesn't boot.

Any ideas? The G.Skill site lists this memory as compatible with this mobo, however the MSI site does not list this ram as compatible. Not sure if that matters. Trying to discover the culprit here (ram, mobo, cpu?) - I don't have any problems pushing the processor to 4.7ghz stable with my Noctua cooler. Just frustrating that I can't get the ram to run at the DDR 2666 that it should easily be capable of.

Core i7 4790k 4Ghz (running at 4.7)
MSI Z97 Gaming 5
G.Skill Trident X DDR3 2666 (F3-2666C11Q-16GTXD)
MSI GTX 970

Thanks in advance for any help anyone can provide!!

[GSKILL TECH]

The RAM is capable, but not all i7-4790K CPUs are capable. What is your VCCSA Voltage? Did you manually boost that to see if it can improve stability?

[pr0phet]

I believe I tried that but can try again after work. Is there a recommended voltage to try? Or a safe range?