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."