This question is very subjective to what you plan to do with your system display wise. If you plan to game on 3 1920x1080 monitors or lower res a single GTX 690 should be a great choice, since you won't be using more than the allocated 2gb of Vram per GPU. But if you want to run 3x @ any higher 2560x1440. Example: 7680x1440 displays you're going to need more Vram allocated to each GPU, in this case a GTX 680 4Gb SLI would be the right choice.
There really is no good legit review.I have seen giving any reason to buy 4GB cards yet imo seems pretty much is based on blanket statements or a bunch of hype.Also, games that actually need more than 2GB of VRAM tend to be GPU demanding like Skyrim with ENB mods http://www.computerbase.de/artikel/grafikkarten/2012/test-nvidia-geforce-gtx-660/23/ and Metro2033,ARMA II,Witcher 2 with Ubersampling,Far Cry 3, are the only ones i can think of. Pretty much the only thing that increases the need for vram is higher resolutions or extreme AA situations. EDIT- Found a review QUOTE: Conclusion
Increasing the amount of memory on board of GeForce GTX 670 and GTX 680 cards translates to obvious performance benefits only in specific unique cases, such as triple-monitor set-ups with 3240x1920 resolution and enabled antialiasing. Metro 2033: The Last Refuge and Sniper Elite V2 are the only games that need more than the standard 2 GB of graphics memory, but the contemporary High-End graphics cards are anyway too slow in these games even with 4 GB of video memory. In the rest of our games we could hardly see any difference between GeForce GTX 670s with 2 and 4 GB of memory in 3240x1920 and no difference at all in 2560x1440. So, purchasing a 4GB card wouldn't be worth the investment unless you've got a triple-monitor configuration. But if you do have one, 4GB graphics cards really make sense for 2-, 3- and 4-way SLI configurations and playing contemporary games at high resolutions. In this case, the increased amount of memory would not become the bottleneck.
As for the particular product, the EVGA GeForce GTX 670 Superclocked+ 4GB is a well-made card that follows the reference design with minor modifications such as the shape of the vent grid and the increased GPU clock rate. By the way, EVGA played it safe with the GPU, which actually turned out to have much better overclocking potential. The memory chips could have also been overclocked to 6608 MHz, for example. The product definitely deserves high scores for its good accessories, handy software tools (Precision X and OC Scanner) and 3-year warranty. Source:
http://www.xbitlabs.com/articles/graphics/display/evga-geforce-gtx-670-4gb_11.html
The more sensible choice is $280 Sapphire HD7950 + OC (amazing bang for the buck). If you want NV for personal reasons or PhysX/CUDA, etc. try to catch a deal on an after-market GTX670 card. For example, MSI GTX670 Power Edition with can be had for $344 after $20 MIR and $15 off. Those are very close in performance to a GTX680 minus the price premium. Newegg had $330 GTX670 Windforce 3x on sale recently. That's an excellent card. I even consider the Asus 680 Top (overpriced) the GTX 690 it's just highway robbery imo needs to come down in price two hundred or so before even considering lol.
Anyway check these out
http://www.youtube.com/watch?v=WUoxv4HWoDM&list=PL13F5266778601CBA&index=16
http://www.youtube.com/watch?v=rk-0ocHYl8g&list=PLFF65661B86D4458E&index=2
http://www.youtube.com/watch?v=IrOYkXrxzjY
Asus GTX 670 DirectCU II TOP - 10.0 rating (only card ever to get a 10.0)
http://www.techpowerup.com/reviews/ASUS/GeForce_GTX_670_Direct_Cu_II/33.html
Gigabyte Windforce GTX 670 OC - 9.8 rating
http://www.techpowerup.com/reviews/Gigabyte/GeForce_GTX_670_Windforce/33.html
MSI GTX 670 Power Edition Twin Frozr IV - 9.7 rating
http://www.techpowerup.com/reviews/MSI/GTX_670_Power_Edition/33.html
They didn't do the EVGA so...
http://www.guru3d.com/article/evga-geforce-gtx-670-sc-review/23
EVGA SC Boost Clock is 1046 out the box...stable at 1200 Mhz
EVGA SC gets 3DMark Score of 8691 out the box and 9443 OC
Idle temp is 29C / load temp is 78C
Noise is 37 dBA Idle / 43 dBA under load
http://www.guru3d.com/article/asus-geforce-gtx-670-directcu-ii-top-review/23
Asus TOP Boost Clock is 1137 out the box ... stable at 1280 Mhz
Asus gets 3DMark Score of 9340 out the box and 9839 OC
Idle temp is 30C / load temp is 72C
Noise is 37 dBA Idle / 38 dBA under load
That makes the Asus 7% faster out the box than the EVGA SC, 6C cooler and almost 1/4 as loud under load (every 3 dBA is a doubling of sound level). The FTW is slightly faster than the SC, leaving the Asus model w/ just a 5% performance advantage.All these cards are solid choices and a pair of any would be much better bang for buck then a GTX 690.
ASUS GTX 670 TOP
MSI GTX 670 PE
Gigabyte 670 WindForce OC
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/56546-msi-gtx-670-power-edition-oc-review-20.html (670 PE OC)
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/55270-asus-gtx-670-directcu-ii-top-review-20.html (ASUS 670 TOP OC)
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/54705-gigabyte-gtx-670-windforce-oc-review.html (Gigabyte 670 WindForce OC)
EVGA 670 FTW!Is a good choice as well.