Sounds like you either need to turn off SLI or use MSI Afterburner to increase the voltage on your 580's.

Also, I kinda noticed back when I was running the few tests I did that when you teeter so close to the VRAM limit while multiboxing crashes can happen. My 580's have 3,072 MB of VRAM and I can never reach that number. I usually reach about 2,900 MB before it begins swapping textures with the SSD. I say this because you mention that you're reaching 1.4GB and that's probably very close to the limit (if not the​ limit) of your 1.5GB 580.