Originally Posted by provost
For surround, you gonna need more gpu horsepower to run three screens before you start hitting a VRAM wall.
Depends on resolution. With 1080p screens 2 GB should be plenty and then some headroom as well as long as you don't overdo AA to some silly level. Performance wise you can go all the way up to 4 cards while vRAM amount is constant and there's nothing one can do about it other than getting a card with more vRAM. I can see one hitting 2 GB limit when doing higher end surround, like 3x 2560x1600 or even 4K screens, for example. In my experience (with eyefinity) when being conservative you can drag 1 GB as far as 4 x1080p and with 2 GB 5x 1080p is not a problem. When you are not conservative (i.e., light AA, good shadows, etc) you can approximate halve those "rules of thumb" so - about 2 GB should be enough for 4x 1080p and sliiightly short for 5x1080p (or equivalent higher resolution screens). So far I have not been hitting the vRAM wall with 5x 1080p with 3 GB of vRAM (and encountered it rarely with 2 GB and almost always with 1 GB).
Now surround is a bit more limited than eyefinity in this regard ofc as its up to 3 screens, but with high end 3 screens one can still go above the number of pixels present with 5x 1080p (~10 megapixels).
So - what I want to say is that this 4 GB can be sensible investment for people doing higher end eyefinity setups or aiming at gaming on 4K resolution with some AA or a memory intensive mod or two. Most likely such undertaking would involve some kind of SLI (potentially all the way up to 4 cards) depending on desired GFX settings and resolution used.
Edit: I should add that one should take GPU-Z memory usage number with grain of salt. It can report your vRAM full but it does not mean you are hitting the vRAM wall. When you really run out of vRAM its in my experience straight trip off the cliff down to ~3 fps - its the best way to tell you are out of vRAM. Just sudden rapid drop to single digit fps. When you just run out of performance by giving card more than it can handle then the performance degrades in a more graceful manner.Edited by Carniflex - 7/20/13 at 10:05am