Im getting a 45w 2560x1440 monitor as well. Was just starting to wonder if I got enough power?
750 is fine. Your max power draw is around 493 watts. Also, keep in mind your monitor doesn't plug into your power supply, so it won't affect your wattage needs
You don't ever want to be right at your max draw on a psu. Makes it very inefficient and hot (wears out faster).
750w is a perfect amount for doing as much OCing as you'd ever want with a nice amount of headroom built in.
493 is nowhere close to 750....?
I realized that after I wrote that :-) thanks.