Some help needed with issues on a pair of 670s

I've been struggling with some issues with my graphics cards for quite a while now and i dont know what to do any more, really

My setup is Rampage IV Extremel, 3930k, 16GB Corsair Vengeance 1600 new ones are Vengeance Pro 2133, Vertex4 boot drive and a pair of Asus 670's DCII in sli

I get frequent nvidia kernel driver crashes which im at the point that i dont know where they are coming from. They usually occur right after heavy load. They will rarely hit while im playing a demanding game (Skyrim, Battlefield, you name it), but as soon as i close the game a crash -or maybe even 2-3 in a row- will occur in the next minute or so. Exception is League of Legends where i never get crashes after the game, rather, during.

First i get a frozen image and maybe some pixels off-color (usually red now that i think of it) for a few fractions of a second then the monitors (2x qHD) turn black/no signal and then the whole thing recovers as it was.

This was happening both before and afteer a clean windows installation. A few months later i tried wiping the drivers once more, completely and reinstallin but nothing did it. This has been happening through several different drivers versions.

I tried testing the RAM, The previous kit (vengeance) gave some errors both in win memory diagnostic and memtest86+. So i baught a new kit, 8gb (2x4gb) Vengeance Pro 2133, and for a start i run them at 1333. They passed through memory diagnostic just fine (hadnt had the time for memtest yet, they are literally about an hour old). No matter what settings (stock, xmp, custom) the crashes still keep happening.

Card clocks dont seem to be an issue as this happens both OCed, stock or even underclocked (both core and vram)

CPU is running at stock speed with no weird tweaks, just the RIVE's defaults.

Power cant really be an issue as i have an AX1200 (definitely overkil but..yeah), unless there is something important i might be missing here, such as psu rails (which just occured to me)

I'm not running the games in surround, only single monitor, and the problems had started even before these monitors, with a single 1080p display.

The cards are positioned in the 1st and 3rd PCI slots, and there is a Xonar Phoebus on the 4th.

I really cant think of anything else to mention here, soo yeah, that's it. Any help or advice that'd help me here would really be greatly appreciated