I'm currently using a 1280 x 1024 monitor that I got with an old system I purchased back in 2006 (in fact I only stopped using the Pentium D system last year as it was a proper workhorse for the programs that I ran) but need to upgrade as I just don't have enough screen space compared with the 2 16:10 screen I have at work, I use one for the main workspace and the other for tool pallets and secondary windows in programs like 3DS Max, Inventor and CS suite.
I don't have room for 2 16:9/10 21.5" or 24" monitors (unless one of them is in portrait orientation so I've been looking at the monitor below at is has the conventional 2560 x 1080 21:9 display shrunk from the normal 29" to 25" for £100 less. Double my current screen space for not much more than a decent 16:9 1080p panel with 30% more screen space over that too.
What is it like to work on one? I've found working on 16:10 monitors at work a little frustrating as by the time the menu bar across the top is take into account the workspace is very stretched out an often the things I'm working on are not of a similar aspect ratio. I used to use 2 Dell 1600 x 1200 panels at work which I dearly miss.
I used a LG34UM95 and i took it back for a few reasons, but gaming is amazing but stresses a tiny bit more on your GPU. Two monitors i think is better but as you said you cant then ultra-wide is a good compromise. and at 25" it would still look good graphically. I would recommend a 1440p monitor if you could fit a 27" just because when editing i find it so much easier as i have lots of room resolution-wise and it keeps the standar 16:9 ratio, but with gaming if your GPU cant handle it then it can look bad scaled down. But its up to what you prefer at the end of the day!
I've got a GTX 760 4GB so I don't really want to go up to 1440p as I'll either have to dial the setting down or play at around 30fps (ugh) plus the cheapest I can find is around £400, twice the price of that LG but in reality probably isn't twice as good. I can fit up to a 29" ultrawide on my workspace but most of them start at £300 for the same resolution as the 25" LG. I was also thinking that with the increased PPI of the 25" I could dial back the AA settings without looking any different?
Everyone else at work is upgrading to 1440p monitors soon (I wont be as I don't don't think I do enough artworking/graphic design to justify the upgrade so I told them to save some money) and I was going to add a third monitor but put it in portrait orientation to see how my workflow is affected, if its good I'll go with 2 1080p panels, one landscape the other portrait.