So i currently have eyefinity running. I have a couple of 24" Samsung monitors with a 16:10 aspect ratio at 1920x1200 resolution.
I used 2 additional monitors for a total of 4 of these before i dumped Nvidia for Eyefinity, sold the other 2 extra monitors (they were 22") and i picked up a 23.4" display running at 1920x1080 or 16:9 aspect Ratio. So i use the new monitor in the middle and the 2 slightly larger screens on the side.
Everything runs just fine, I run windows with the 2 samsung 24" at the full 1200 vertical pixels and its just a touch taller on the sides, when i play games in eyefinity, i run at 5760x1080 and since those 2 side displays are all extra and the middle monitor shows everything just as it would without the side displays, it does not distort or anything.
So no the 23" would not look stupid, but your going to come across the same issue with the 1200 vertical pixels vs the 1080 on new displays but its really not going to impact anything in a negative way. When you line up your displays, i set windows to be flush across the bottom of the displays so the extra pixels are just at the top of the screen.
This is my eyefinity display while in Modern Warfare 3. Since the game does not support that mode i use a handy little application called Widescreen fixer which i would recommend you get. You basically download the game files to whatever game you want to play and then it will fix your display via a hotkey. You can see how my display stretches across all 3 displays when it thinks my eyefinity is only 1920 wide and then i toggle the widescreen fixer hotkey to get the apropriate 5760x1080 resolution