I had heard rumors of X79s having problems with some of the Vengeance RAM. In looking around, I would say it is a bit more than rumor.
Now I don't know what series of Vengeance is causing problems. I am sure Corsair uses more than one different type of memory chip on their sticks depending on speed, series and voltage. Some specific types/brands of memory chips play better with certain chipsets. With your setup and 4 RAM channels, the speediest/lowest latency stuff is overkill, well, maybe except for benchmarking. If you want to troubleshoot it, relax timings and speeds and see if anything improves.
To the point, when I think of memory problems, I look at BSODs, lockups, no boots, missing memory, and failed memory tests as signs of a memory problem, not really game stutters.
Your symptoms could be caused by CPU/GPU throttling, some program hitting your CPU at odd times, some program trying to access hard drives/SSDs while the game is running, or glitches with the games themselves. Just recently I installed the latest and greatest NVidia drivers for my 780, and I will swear I now have an intermittent stutter in Borderlands of all things. (Bought Borderlands a few years ago and never even installed it, but now I have to go through it). With your system, SLI 690s, if there is a driver problem, your setup will sure as heck find it.
I am a retired Ford tech. Next to Fords, any computer is a piece of cake. (The cake, its not a lie)
3770K @4.5, Corsair H100, GTX780, 16gig Samsung, Obsidian 700 (yes there is a 700)