Those types of monitors are targeted more toward enthusiasts whom plan on spending north of $2500 on a system. It's a bit ridiculous for someone who spent $1200~ on a system to then purchase a monitor for more than half that for gaming.
Unfortunately, your system won't do well at 4k. 960SLi should run okay with 1440p, though. For a gamer in your position, I'd suggest you just purchase a 120Hz+/3D monitor at 1080p and enjoy the higher refresh rate. The higher resolution isn't worth the decreased performance for you. Lower settings (aka. lowering details to raise FPS) will contradict the resolutions purpose of increasing details in the first place. Just avoid 4k altogether.