Basically it depends if you have multiple monitors or a single monitor simply because when the calculation that happens in the
GPU so that many pixels appear on screen to form the whole screen they must have storage to be saved in the card, so
guess what the storage is... that's right you guessed it, it's the VRAM.
So if you have multiple monitors I highly recommend the 6gb version.
E.g. you have a 2GB card and you're running a high-end game at ultra settings you're going to get FPS drops if you're running a second monitor at the same time in the same graphics card.
3GB is solid for 2 monitors but that depends on their resolution and if you have one using the HDMI port because HDMI is harder on the card than DVI. Same goes with the FPS when comparing a 60 Fps monitor to a 120 Fps monitor and if the game is or isn't locked to 60 Fps.
But as far as no game using more than 2GB is wrong;
Heavily modded Skyrim littered with custom HD packs etc can use well over 4GB of VRAM (not including System RAM).
Watch Dogs on ultra settings will use 3.4GB of VRAM (not including System RAM) and that is without unlocking the hidden graphic settings that were only shown at E3.
That's just a few examples and you can look it up too; with GPU statistics showing a GPU maxing out at 4GB VRAM with one monitor playing one game.
Not all games will use more than 2GB but some games do and games within the next 2-3 years will use more than 2GBs also.
That and with the 280x 6GB having 10 degrees less then the 280x 3GB version on load you can overclock it further.
Also if you want to use Crossfire or SLI make sure you have a good CPU and depending on the cards have the CPU Overclocked above 4Ghz and above 4.5Ghz at the least if you Crossfire / SLI 3 high end cards, GPUs can only work with what they are given and it's the CPUs that feed them the game (the GPUs cannot access the hard drives directly it all has to go through the CPU same goes with the system ram anything coming in and out goes through the CPU hence why it's the heart of a computer) and if you have 3 Crossfired / SLI cards and a CPU lower than 4Ghz your CPU will choke your GPUs the they will drop frames not perform as good as they can and stutter but they will still run at high temps though even if they aren't being fed what they require.
E.g. Two R9 290s on CPU lower than 4Ghz gets choked and will run Crysis 3 at 30-40 fps however One R9 290 will run at 60 fps on Crysis 3 with the same settings on the same CPU. because having Two Crossfire R9 290s is too taxing on a CPU lower than 4Ghz.
