It should be perfectly possible

Just use autoexec.cfg to set the height and width whatever you want

seta r_mode -1
seta r_displayrefresh 144
seta r_customwidth 1920
seta r_customheight 1080

Now remember that vertical fov is locked with the exception of changing aspects eg. 4:3 and 5:4 may be slight different vertically but thats just the engine compensating the aspect difference.

I have previously tried with a single monitor something like 1920 * 640 and I got the wide effect so it should not be any different with 2 or 3 monitors or a widescreen unless you run into trouble with the primary/secondary screen not aligning correctly but that should also be easy to solve.

If you have not bought the widescreen monitor yet I would suggest try like i said 1920*640 or 768 or 800 on your current screen. That should give you a rough idea of what will happen with a ultra wide minus the black bars top/bottom. Also consider if this widescreen is not a fast 144hz screen then you will probably still suffer against those who have 144hz despite your extra view.

Also here is a video quake 3 on a 360degree display which also gives a rough idea of how this all works. They just seem to have a very low FOV like 60 or something in that video which is why it seems like the top is cropped. That should not happen at your normal resonable fov because vertical fov is constant.
https://www.youtube.com/watch?v=Cqh_F4iN8pg

Edit: I guess I could say more if you can follow this:

4:3 aspect = 12:9 aspect (same ratio)

so when you use a 4:3 screen @ 90 fov you hit 90 fov at edge of the monitor

When you use 16:9 you hit 90 fov at 12:9 of the monitor

Now when we move onto 2560 x 1080 which is 21:9 I would make the assumption that vertically 21:9 is the same aspect as both 4:3 and 16:9 vertically - therefore you will still hit 90fov at a ratio of 12:9 (the centre of your screen) and then you will just get more on the edges to fill out all the way to 21:9

ok i have read some tests and people claim that dispite having a reaction time of 1 ms they have ghosting issues. Plus they are expensive. So i guess i go with a normal monitor instead.

"dispite having a reaction time of 1 ms"

1ms is generally talking about grey to grey pixel response time which is NOT an indicator of how much the screen lags AT ALL. (marketing lies)

Lag comes from the internal circuitry (Scaler PCB board) which is often about 15 to 40 milliseconds despite most monitors saying 1 or 2ms pixel response but conviniently ignoring Scaler lag where the real delay occurs.

"they have ghosting issues"

An over rated problem. People say Benq XL2411T has ghosting issues but if you ask me its a fine monitor. There is a little ghosting but there is no situation where you will get confused shoot at the wrong ghost image.

"So i guess i go with a normal monitor instead. "

Define normal. In general all the 1080p 144hz monitors have near zero scaler lag. You need one of those if you want to play FPS games even slightly competative.

They do make 144hz screen above 1080p now - but you just should find info on the amount of scaler lag they have which im sure some people have dug into.

Ah ok the scaler lag is a deciding thing. Thx i will research for it!

"dispite having a reaction time of 1 ms"

1ms is generally talking about grey to grey pixel response time which is NOT an indicator of how much the screen lags AT ALL. (marketing lies)

Lag comes from the internal circuitry (Scaler PCB board) which is often about 15 to 40 milliseconds despite most monitors saying 1 or 2ms pixel response but conviniently ignoring Scaler lag where the real delay occurs.

"they have ghosting issues"

An over rated problem. People say Benq XL2411T has ghosting issues but if you ask me its a fine monitor. There is a little ghosting but there is no situation where you will get confused shoot at the wrong ghost image.

"So i guess i go with a normal monitor instead. "

Define normal. In general all the 1080p 144hz monitors have near zero scaler lag. You need one of those if you want to play FPS games even slightly competative.

They do make 144hz screen above 1080p now - but you just should find info on the amount of scaler lag they have which im sure some people have dug into.

Yeah I have an ultra-wide with 2560x1080 res, but I play in 1920x1080 centered because it doesn't scale the vertical fov properly and I couldn't find a fix.

I have started to really enjoy the ultra wide format. Unfortunately my ultra wide monitor just doesn't have high enough refresh rate to for it to be viable for FPS games.

Refresh rate does make a big difference. Switching my screen from 144hz to 60hz it immediately feels lagged and as if something is just plain wrong.

The point I was trying to make to above poster tho - 60hz screens are generally paired with junk laggy Scalers by manufacturer

144hz screen are generally paired with a very fast Scaler.

Even the pro street fighter players are very picky about this and started compiling lists of 60hz TV's with fast Scalers.