I started playing games across triple screen this year and I have to say it always puts a smile on my face. However Ive started to notice games are not running at a frame rate I would be happy with 40+ frames.
Thing is Im running the games at max settings with vsynch. A lot of games are fine. Max payne 3 ran awesomely, Guild wars 2 very good and ive had no problems with racing games.
Sorry I will get to the point.. The last few releases Ive picked up haven't ran great.
Farcry 3 at max settings with no AA running at 5760 by 1080 runs around 18fps to 35fps.
Your graphics card needs to push a bunch of pixels.
I think a second GTX680 would do that part of the job.
A 2600K overclocked is almost as good as it gets for gaming.
But, To help clarify your options, run these two tests:
a) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely cpu limited.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 50%.
This will simulate what a lack of cpu power will do.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
set to 50% and see how you do.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.
It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.
And... you might try to experiment with disabling hyperthreading.
You might get a slightly higher overclock.
Also, some games are not hyperthread aware, and might be dispatching game code on a hyperthread which is less capable than a full thread.
Far Cry 3 is very demanding on a single 1080/1600P monitor, GTX 680 scored 35 FPS in the 2560x test with just high quality preset & 2x MSAA enabled as reported by guru3d.com, so don't expect 40+ FPS using GTX 680 SLI at such a resolution.
Now, the most important note you should know is that Far Cry 3 isn't yet scaling well on CF or SLI, 90% of the players reported the second card being used around 30% or 40% while the first card is being utilized 99%. So I believe you could achieve very high FPS if they provide the proper drivers and patches.
I run games at 5760x1080. I have a new i7 3770k and 2 old GTX470s in SLI. Bottom line is 5760 is a huge res and needs alot of gpu power. In order to get my system working perfectly i had to do some tweaking. I first wondered what component was struggling. Was it ram usage, cpu time, or GPU? I set riva tuner to logging mode and played a bunch of games while logging CPU utilization, GPU utilization, ram usage and temps. I played a bunch of rounds of MW3, Blops2, Mass Effect 3, planet side 2 beta, even a few older games like killing floor. CPU usage was always around 25-50%, the highest I ever saw the ram usage go was around 6 gigs. Both video cards were always around 90-100%.
I learned that 3 screens at 5760x1080 takes a huge amount of gpu power, much more than I thought. At this point adding a second video card would increase your FPS by 80-90% in games that have a good working SLI profile.
Only other way to get higher frames is to lower detail settings in game. Both of my 470s can overclock from 607mhz to around 700mhz alone but when they are in SLI I get driver stopped responding with any thing more than like a 1% over clock.
Nvidia does a pretty good job at making sure all new games get profiles rolled into the drivers. You just need to keep the drivers up to date.
For Far Cry 3, I would suggest shelving the game for a month or two, it's new enough that driver optimizations probably haven't been made for it. If you come back in a month or so, your framerate may be more to your liking; that said it's a very demanding game, even with SLI you may get less FPS than you want.
Personally, I wouldn't buy another video card for one game unless I was playing it all the time, as long as 90% of games meet your desired quality and smoothness, and forget about the outliers (maxing the most demanding game is more or less bragging rights, and very minor benefit to your experience). If you're not happy with performance in several other games, then maybe SLI is a good option. (As an example, MechWarrior online murders my 7870/2700k combo, but it's more because the game isn't very well optimized than anything else; for that one game, I live with the 20-50fps, because it's not worth fixing a software issue with hardware).
I don't find it too surprising that triple monitor gaming doesn't add any extra load to the CPU, from all I know about rendering (as a programmer only a bit of basic 3d experience), the resolution is nothing more than a setting as far as the CPU is concerned, the CPU doesn't have much (if any) extra work for an increased resolution; field of view could have some impact, but I'm inclined to think most of that is also handled by the GPU.
Also, it's worth noting that CPU utilization numbers of 25%, 50%, 75% do little more than indicate how many cores of a quad core CPU a game is fully utilizing (and numbers that fall in between usually indicate the game offloads some minor tasks onto another core), higher clock rates may still improve performance if your CPU is at 25% utilization because the game is only utilizing one core of the CPU, increasing the clock speed will allow the game to execute more code on that single core of the CPU.