argh, damn it, i can't decide between u2913wm and u2713hm....it's killing me!
I'll help you out here. Get the U2913WM because it's 1337.

I'm sure you've gone through all of this but the main differences are of course size and resolution. The colour performance, contrast characteristics, screen surface and responsiveness is largely comparable for both.
Physical size differences - the U2913WM is a fair bit wider (slightly wider than a 30" 16:10 monitor) whereas it's also a fair bit shorter. A nice little visual comparison of the screen size difference - http://www.displaywars.com/28,75-inch-21x9-vs-27-inch-16x9.
There are the same number of pixels horizontally on both monitors, but they are tighter together on the U2713HM due to its size. The U2913WM has fewer vertical pixels but less height to spread these pixels. Overall the U2713HM offers the tighter pixel pitch - 108.79PPI for the U27 vs. 96.64PPI for the U29.
It's really a matter of opinion as to which will offer you the more engrossing experience when gaming, watching movies etc. And which size you will prefer for just general desktop browsing. You have more real estate on the U27 but the ultra-wide aspect of the U29 is something that many people really love. It's something quite different.
i always appreciate your replies. in this case yes, i have thoroughly researched said subject. i have had some 27"monitors before (namely the Fujitsu P27T-6, which i returned as i didn't have a machine to fully take advantage of it at the time), i just find the 21:9 aspect ratio very intriguing and as the main use of the monitor will be gaming and watching movies, it might be really awesome.