If I get gtx 680, then will I still be able to play games like crysis at maximum settings at 45 fps+?
Was that even a question or were u just kidding? Crysis will run just fine on 680, and even Crysis 2 will run fine with 680 even with the DX11 patch(the game was a console port so they didn't max out graphics and improved their engine). I also bet Crysis 3 will run fine(30fps+) on 680 since it is also going to be console port.
It is better that u spend that money on other pc components unless you are super rich like bill gates.