I really don't know how it would work for mixing, but I actually use 3 monitors (sort of) for work.  I have a 14" laptop that is almost useless except as a place to keep my email in case anything hot comes in.  I have a 27" monitor mounted on an arm directly above that, and a 32" monitor sitting to the left. 
 
That arrangement works well for me doing database programming and building analysis and reporting tools.  I really think of mine though as if I had 2 monitors that I actually do the work on, and the little tiny laptop window is just there for the emails. It is way too small for any real coding or development work.

I'd think about how you want to work... and don't forget about ergonomics.
ie: You don't want the video monitors messing with your studio monitor speaker position.
 
I'd want at least one large video monitor (between my nearfield monitor speakers).
A single/large 4k video monitor fits nicely between a pair of nearfield monitor speakers.
If you try to squeeze two large video monitors between the nearfield monitor speakers, they'll be too far apart.
 

To avoid the problem Jim mentions, I have gone vertical stack with my two monitor set up.  My top monitor is a bit too high but I am starting to look a solutions to allow me to angle my bottom monitor to something lik 30 degrees which would be cool since I put console view on it mostly.

BobF
I went with a single 43" 4K, which is the same as 4 X 1920x1080, a while back.  I will never go back.
 
I still have one of my 1920x1080 off to the side for ancillary use, but for the DAW it's the big, single display all the way.

Yeah, there's no way I could make a monitor that large fit in my 11'x5' studio! I'd have to give up my near field monitors!

Thanks for all the info. I should say that I'm not sure, and I'm not in the studio now, but I don't think my GPU will work with 4K--at least it won't take advantage of the full 4k resolution.
 
There should be a punch-line after I say, "My studio is so small..." but I am seriously grateful for it. It's just forced me to really plan everything out to make sure it fits, and doesn't interfere with what's most important with mixing and mastering - which of course is sound. If it wasn't for the stands from places like Digital Tigers, I probably wouldn't even be able to think about 3 decent size monitors.
 
Cheers
 

razor

BobF
I went with a single 43" 4K, which is the same as 4 X 1920x1080, a while back.  I will never go back.
 
I still have one of my 1920x1080 off to the side for ancillary use, but for the DAW it's the big, single display all the way.

Yeah, there's no way I could make a monitor that large fit in my 11'x5' studio! I'd have to give up my near field monitors!

razor

BobF
I went with a single 43" 4K, which is the same as 4 X 1920x1080, a while back.  I will never go back.
 
I still have one of my 1920x1080 off to the side for ancillary use, but for the DAW it's the big, single display all the way.

Yeah, there's no way I could make a monitor that large fit in my 11'x5' studio! I'd have to give up my near field monitors!

Horizontally, this display is almost the exact same size as the 2 x 21.5" it replaced.  It is also twice as tall, which usually isn't the limiting direction.
 
I chose this size so the display could be the same distance as those it replaced, maintaining the same physical size of objects on the screen.  I probably could've have a bit smaller, maybe even 39-40", without inducing eye strain, but I didn't want to risk it.

A quick thought ...
 
You could always get a big 4K with a height that matches your available horizontal space and run it in portrait, turned sideways.
 
I haven't done this with a 4K, but I have with a 21.5" 1920x1080 to view PDFs.
 
Just a thought that might save you some bux and simplify the mounting, while removing display frames.

I have a 27" 1920x1080 monitor. I can see really well with it. It's large enough to have all trks I need on the screen. I use Screen sets profusely. So even though I still have one of my 19"  monitor on the side, the only thing I put on it is the RME mixer. I do everything on the 27". 
 
Oh and I use the second monitor for putting up lyrics too. Other than that, it's just used on 'as needed' basis. 

The answer from me to the OP: It depends.
 
I think it depends on several things such as the type of monitor doubled or tripled, the size of the bezel, the aspect ratio, the distance from the sitting position, the amount of desk space you have, and distance/space available between your speakers.
 
Up until now, I ran with three monitors. One Dell U3014 30" 16:10 for my main, center display and two, older 24" 16:9 Viewsonics on each side. It worked, however, my speakers were being partially mask by the outside monitors.  My room and setup could not allow much wiggle room to push the speakers (on stands) further out and back. My desk also isn't very deep. Only 30" front to back so I couldn't push the monitor "wall" back further to get it behind--or in line--with the speakers.
 
Fast-forward to about a week ago. I found and bought a nice, used Dell U3014 for a good price.  My intention was to ditch the 3-screen setup and go with 2...two 30" 16:10 displays.  Well, the bezels on the U3014's are a bit much, when doubled, and due to the constraints of my desk and speakers, the only way I could configure them is side-by-side, directly in front of me.  It just felt awkward.  Centering one monitor and putting the other to the side was extremely awkward.  IMO, these monitors are just too big and tall to run a multi-monitor setup on a normal desk with limiting factors.
 
So I'm down to one display.  One 30" U3014.  I use Live, so flipping between Session and Arrangement views works well with one monitor anyway, so no sweat there.  However, I think I will miss the other monitors for plugins and VST's, which were frequently filling up the space on the 2nd and 3rd monitors of the previous setup.
 
 

Would a 27 give you the same real estate as 2 x 22's?
I see this on line
https://www.staples.com/H...onitor/product_2720259

Is that resolution too low?

I'm faced with sharing the two 22's been a laptop and a new desktop in picking up. Figured a single monitor would simplify that.