Allegedly people learn from mistakes. I promise I'll start too. That's the second time I'm setting up dual display at home. I guess it's a scenario similar to what other people go through - for some time you have just one display A, then you buy display B, then you need to move and decide not to keep A anymore and happily live with B only for a while. Then you want to go dual again (because let's face it - it is convenient), and buy display C.
Be damn sure you have exactly the same models. Same manufacturer, same size, same model. Otherwise it's just pain in the ass. I know it's difficult if you buy them tens of months apart - you probably won't be able to buy exactly the same model as you're already using, because manufacturers "moved on". But try, try really hard.
I've just finished setting up C so it displays images as similarly to B as possible - I couldn't make it exactly the same. I know it's gonna be irritating for the next few months, until I get used to the difference (hopefully I will, eventually). And it was just the colours! Different sizes are also frustrating, not only physical dimensions, but also pixel pitch - the same 400x400px window is bigger/smaller on the other display.
Photography is my hobby, and I try not to invest lots of money in my gear, that includes PC I use for postprocessing. It has to be functional, I try aiming at stuff with best bang/buck ratio, but I'm not gonna spend $4k on pro-graphics Eizo computer display.
I think I've finally learned my lesson, next time I'm gonna buy two exactly the same displays. Really. Third time's the charm.