Wait just a damn minute here. Why are people PRETENDING that a single Titan has 1080p mastered? It does not by any stretch of the imagination. Try Crysis 3 maxed @ 1080p with a single Titan = have fun with dips into the 20's.
OP, a single Titan is adequate for Far Cry 3 @ 1080p but its nothing like overkill. You'll likely see around 60fps with dips well below. Heres my solution for you and you better believe its THE BEST ONE:
Sell the 680 & buy two 780's. It will end up costing a couple hundred more than a Titan but will be way way faster. That's the thing to do brother. 3gb of ram is enough for 1080p for a long time.
Let's also make something else clear here. Why are people PRETENDING that maxing every single item in the game is a pre-requisite? Now i'm not saying to do anything drastic. However - you can lower one, two or three items in most of these games and THEY LOOK EXACTLY. THE. SAME. with absolutely no difference - except you gain 30-40 fps. Case in point, i've run numerous benchmarks in crysis 3 between very high and high and they look exactly the same among hundreds of screenshots. You'd have to have super human vision with a microscope to spot a difference, because in real world use, there isn't a difference. You don't need 8x MSAA in crysis 3. You get 95% of that quality with FXAA. Additionally, this is applicable to ALL games. You can be benchmarking nerd and benchmark Metro 2033 with every setting maxed, again - just because someone wants to be ridiculous and do that doesn't mean there is a difference in the appearance of the game. You can gain 20 fps just by turning ADOF off. This same concept is applicable to crysis 3 , far cry 3, or whatever. People who max every single item are just benchmark nerds. You don't need to play a game like that, when you can lower 1-2 items, get the same visual quality, and gain 30 fps.
This also completely ignores the fact that there are like 4 games like this. Out of a gabillion PC games. So I guess this all boils down to whether someone is a benchmarking nerd or someone who actually plays games. I actually enjoy playing games. Titan is great for benchmarking, but it IS overkill for 1080p, period - you don't need 6GB for 1080p. I personally enjoy playing PC games, I could care less about how well they benchmark with something absolutely stupid such as 8x MSAA. I don't get some sudden sense of pride playing a game with an absolute overkill setting when it isn't needed. ESPECIALLY when it makes no difference in terms of visual fidelity.