Based on my understanding, Crossfire and SLI does not combine the memory size of two or more GPU. When you have two GTX 680 in SLI, your total GPU memory is still 2GB and not 4GB.
But how does it work on multiple monitors? If I have 6 monitors at 1080p and has three GTX 680 2GB, can it be configured so that each video card is powering only two monitors independently? How about triple monitor setup where each monitor is being powered by one video card? Will all the video cards memory become like 6gb in total?
If you are gaming you want crossfire/SLI. you need the monitors to function as a single display, unless you have a game that natively supports using multiple. If you aren't gaming memory and FPS are irrelevant. and you wouldn't be looking at GTX680s