Oh, not at all! Here's what my xorg.conf looks like: https://gist.github.com/CFSworks/6101954
Note: I'm not an expert at writing xorg.conf's, so please don't use mine as a prime example. Also, I don't know if those timings are optimal, but they do produce pretty stable 120Hz output for me at least.
Note #2: When you use NoEdidModes, the nvidia driver seems to insert 800x600 mode on its own. Using this mode will not work; your monitor will start displaying a bunch of test patterns until you set it back to 2560x1440.