I don't even understand all this ppi hype, nor even dual displays anymore. I always used dual-triple displays in the past but nowaways I just bought a single table-size (49-inch or something like that) 4k display and put it right in front of my desk just to use it in a plain old 100% mode (no "hi-dpi" scaling, just tweaked some font sizes in editors' configs). This way it effectively replaces 4 displays with a single seamless space - no additional frames, no constraints, almost no head turning, beautiful tiling (when on Windows - PowerToys' FancyZones are great).