Multi-screen gaming is called Eyefinity (with AMD cards) or Nvidia Surround (specifically 2D surround) with an Nvidia card.
AMD sort-of allow you to use mixed resolution eyefinity.
My understanding is that this is not possible at all with Nvidia Surround. That requires displays with identical resolution. That was certainly the case when I looked into this a couple of years back
The issue is that Surround (and eyefinity) has really gone out of favour now there are premium 4K, high frame rate and ultra wide displays which most people would consider offer a comparable or better experience without the compatibility drawbacks of multi-screen gaming.
I'd be very surprised if Nvidia had been actively working to improve surround (or enable mixed-resolution surround) in the last couple of years.
Case in point, Nvidia's "Surround" system requirements page still recommends a PCIe 2.0(!!) x16, and references ancient cards like the Titan Z and GTX 590:
http://www.geforce.com/hardware/technology/surround/system-requirements
I don't think it gets a lot of love these days.
TL DR: with an AMD card you could try and do it, but it wouldn't work well even if it did work. With an Nvidia card you straight up can't do it.