The Bottom Line
We've given the ASUS GeForce GTX 670 DirectCU II 4GB video cards plenty of opportunities to prove to us why we would need 4GB of VRAM on these. Unfortunately, these have come short of proving this. We tried pushing a single ASUS GTX 670 4GB to the max on a 30" display, at more than playable settings, and also at 1080p. We saw no advantages with a single card. Then we put two together in SLI and tried to push them to the max at 5760x1200. What we found was that higher settings were possible to enable, but the performance wasn't there to allow them to be playable. Simply, the performance of GTX 670 isn't enough to utilize the capacity of 4GB of VRAM.
This is a shame, because the extra RAM has pushed up the pricing on the ASUS GTX 670 4GB to levels that are near Radeon HD 7970 GHz Edition and GeForce GTX 680 video cards at $459.99. Both of those video cards are clearly faster than GeForce GTX 670 GPU based video cards. So the extra money, doesn't buy us the extra performance we would want. Instead, the extra money, is better spent buying the faster GTX 680 or HD 7970 GHz Edition GPU based video card, to get better performance in games.
To make the 4GB of VRAM on the GTX 670 work for you, you are going to need at least three of them for 3-way SLI, to give you the performance to back up the VRAM. Or, we would also like to see 4GB of VRAM on 2-way GTX 680 overclocked, or even 3-way GTX 680. There are advantages to more VRAM, and 4GB can smooth out performance in a lot of games, but today's games are more GPU demanding than ever. These newer games require a lot of performance, and GTX 670 is already starting to show its age in today's latest games. We are already experiencing today the fact that we need faster GPUs in games like Far Cry 3 and Hitman: Absolution.
As it stands, if you want two good GeForce GTX 670 based video cards, stick with the 2GB models, and save some cash..