144Hz just means it can show 144FPS (Frames Per Second).
However, most games can't reach this without reducing the quality. It varies COMPLETELY from game to game.
You don't want to drop below the target refresh rate (i.e 144FPS) or you get synch stutter issues. If you enable Adaptive VSYNC then it just turns off VSYNC if you drop below 144FPS but then you get screen tearing.
LOOK AT BENCHMARKS for a GTX760 to find what frame rates you can get out of most games. See any above 144FPS?
*My advice looking at your budget is THIS:
1) Get an Asus GTX770 instead (about $320), and
2) Get a cheaper 60Hz monitor. Still a nice monitor for $200 or so but just not 144Hz.
OTHER:
If you want a really awesome experience then consider getting one of the Asus G-Sync monitors for about $400 once released. A little more expensive but so worth it.
Here's a few links:
http://www.geforce.com/hardware/technology/g-sync (*Watch the product demo video)
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/64586-week-nvidias-g-sync-monitor.html
Most people don't understand how significant G-Sync is. You really need to try it. Basically the graphics card tells the monitor when to update which makes gaming much smoother, and avoids the hassle of trying to stay above a target refresh, or suffering the cons below.
It also reduces LAG significantly especially at lower refresh rates.
*You can set a game to 40FPS by using G-Force Experience (defaults to optimal settings for 40FPS) which should be really smooth, or manually tweak a little higher.