I would always take the manufactures specs over a website review, just sticking four cards into slots and shoving a four way bridge on them does not mean that they are going to be running in 4 way SLi.
I've tested many, many games and I can tell you that a single GTX680 can handle most of them at 100% quality (single 1920x1080 monitor) and the rest at almost full quality.
The main exception is PhysX which can be very demanding. As mentioned, I strongly recommend you try the GTX560Ti as a dedicated PhysX card, though you should test for EACH PHYSX GAME. Just run FRAPS during a game and make sure you can maintain 60FPS with everything at FULL, or almost full with PhysX enabled.
You can expect something like this:
1) Diablo 3 - full settings even on the GTX560Ti
2) BF3 - almost full settings on the GTX680 (just tweak to maintain 60FPS)
3) Metro 2033 - an exception. still demanding with a GTX680
4) Batman Arkham Asylum
- turn off DX11 due to severe stuttering.
- GTX560Ti for PhysX should be fine (PhysX causes some stutter with only GTX680).
5) Crysis 1 - GTX680 only for almost full quality (minor tweaking)
6) Crysis 2 - GTX680 only for almost full quality with HD texture pack
7) Skyrim - GTX680 only for full quality with HD texture pack
8) Alice Madness Returns
- GTX680 for full quality without PhysX
- experiment with GTX560Ti for PhysX
- native 30FPS, but Google for enabling 60FPS
*surprisingly good game if your system handles it
9) Assassins Creed series - GTX680 for full quality in all
10) Grand Theft Auto IV - an exception. still can't maintain solid frame rate with even GTX680
11) Shogun Total War 2 - runs and looks great on single GTX680 but tweak for solid frame rate
12) Mass Effect series
- all on highest settings with single GTX680
- *force SUPERSAMPLING AA for ME1 and 2
- *read up on tweaking of ME3
12) Witcher 1 - highest settings (force VSYNC in NVidia Control Panel)
13) Witcher 2 - almost highest settings on single GTX680
14) MOST OTHER GAMES 100% quality on single GTX680
- most games at or near 100% quality on single GTX680
- 2x or 3x SLI is overkill and just adds noise, heat, and microstutter
- GTX560Ti as dedicated PhysX card but EXPERIMENT.
- *take the money earmarked for extra graphics and task to better sound if you don't have it (I love my Auzentech Forte X-FI sound card, and M-Audio AV40 stereo speakers).
Your gonna want to drop the 560 if its 1 gb but perhaps instead of a 680 look into getting an older 590 on ebay or something. It also depends on why you would want to do 4-way sli. If you have a monitor that is 1080 or less you are just wasting a lot of performance.
If you plan on doing 3d, just stay with nvidia hands down 7 time out of 10.
And if you do 3-way or more sli the micro stutter does go away and AMD scales better with its crossfire as you add more cards. The downside is few games actually are even coded to let you use more than one or two cards. Also if you like to use v-sync, find the card that averages or gets a minimum of your screens refresh rate with your resolution. Reason being is that if your getting more frames than your display can show you wont even see the performance in a meaningful way.
*Note the model number. There is a reference Asus card which looks different and one without the "T" which is almost, but not quite as good (the above model has a GPU tested to handle the oveclocking.)
If you don't want a 3-slot there are a few good 2-slot models. MSI has a good one but the above Asus is the fastest and quietest model available.
http://www.newegg.com/Product/Product.aspx?Item=N82E168... This is definitely the 680 to get if you choose to go that way. It is the one I have for now.
A 670 is much more bang for your buck especially if you were to do SLI.
The 600 series has less microstuttering than the 500 series.
If you were to do 2x or 3x SLI with 680s or 670s I would personally recommend to just get a 690. 690s are very very close in performance when compared to 2x680s. With the added benefit of less Power consumption, heat, and less microstuttering. And it takes up less slots and room and if you decide to watercool it'll save you the cost of a waterblock.