How come my 680 lags on far cry 3?

Well, that setup is no more powerful for gaming than 8GB, an i5-3570k, and an overclocked GTX 670, which is able to max out the game at 1080p and 60fps with relative ease.

Sounds to me like you either don't have enough power running to the system or you haven't updated your drivers with ones adapted to far cry 3.
 
When you say lags does the FPS drop? If so have you tried to go into Far Cry in the video quality options and turn "Post FX" to low or medium.

You sure you have the 310.90 drivers that came out 1/05/2013 as these are supposed to increase Far Cry performance 38% for a GTX 680.
 

cooldudesubho

Honorable
Feb 24, 2012
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10,810

Don't lie.You won't get 60FPS with msaa enabled.OP you need to turn of msaa to maintain over 60.
 

kynolin

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Jan 22, 2013
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If by "highest setting" you mean the same as the Tom's Hardware Far Cry 3 benchmark, no 680 can run it. If OP doesn't provide details, nobody can provide reasons.

This is what Tom's Hardware considers the "highest" settings. Which I doubt you have three monitors, but still. That's how few details you provided.

"As far as 5760x1080 goes, forget about playing at Ultra quality with 4x MSAA. We're not sure that there's a rig out there able to deliver perfectly playable performance without some sort of compromise on detail settings."

Source: http://www.tomshardware.com/reviews/far-cry-3-performance-benchmark