I found something with an effective resolution of about 2560x1440 to be a sweet spot, where I can fit windows needed for a single task in one screen. Provided those windows don’t waste too much space with unnecessary stuff of course.
I quickly realized I absolutely hate setups with multiple monitors, when I was given one at work. I quickly gave back my second monitor, because it just made it worse for me, and additionally wasted space on my desk. If you want to improve my circumstances at work, give me a bigger monitor, not more of them.
(I've never even tried multiple monitors. I could immediately think of several reasons why they would not be an improvement for me, so made a quick decision in 1998 and moved on.)