If I didn't have a music mixing/mastering hobby, I'd personally go with 3 monitors horizontally. Main monitor in the middle, smaller peripheral monitors on either side. It helps the neck, believe me. Having to go vertical was only a function of necessity for me, because I've always been in rooms where I needed my speakers to be equidistant to my listening position, so I could never really scale out horizontally. And because I love big monitors, there's really not much I can do to prevent that, short of building a custom desk with inlaid, angled monitors for my peripherals. (which I totally want to do when I buy my house!)
If you're headphones mostly, or just gaming in general with even speakers that don't need to be positioned perfectly in a particular way in respect to your listening position, I'd say it's better to just scale horizontal. Big bad ass screen for the middle, which is your gaming screen, and maybe two smallers on either side that you can rotate vertical or horizontal to adapt to your needs. Swivel monitors are great for this. Then you have all the screen real estate you could ever need, and goddamn the productivity is like 10/10.
__________________
|