What screen have you used so far?
For desktops, Apple define a Retina display as 220 Pixels per inch. Normally, Apple defaults to run these at a 2x setting, resulting in an effective PPI of 110, but with much smoother font rendering than a standard 110 PPI display.
For a 27 inch display, a standard 1x resolution is 2560x1440 resolution. E.g. Dell U2711 etc
A standard 2x display is a '5K' display with 5120x2880 resolution. E.g. retina iMac and LG superfine.
The potential problem with a 2x Retina display is that they have 4x the number of pixels, and thus take 4x the graphics power. As a result, if you are sensitive to smooth user interface animations, you may find that animations like window resizing, full screen etc, on the Retina display are a little 'choppy' with frame rate dropping from 60 frames per second to 30 or even lower. For integrated graphics, more RAM has been reported to improve performance. Also a dedicated graphics card will help a lot.
Note: some people prefer smaller font rendering than 110 PPI, and some prefer larger e.g. 95 PPI.
95 PPI is the default for a 1920x1200 or 1920x1080 24 inch monitor.
These are ideal as new '4K' monitors (3840x2160) run at 2x scaling to get the same 95 PPI, but smoother fonts.
Again, the stress on the GPU is 4x that of a 1x monitor, but still about half the total number of pixels as a 5K display.
Finally, you could chose a 4K 27 inch (or larger) display. Here is gets a bit more complicated.
At 1x scaling (3840x2160 effective resolution), the PPI will like be too high for many users. The fonts will be pretty small. But some users like it.
Additionally, at default 2x 'retina' scaling, the effective PPI, will be too low, with very large fonts, the same as a 27 inch or 32 inch 1920x1080 monitor.
In these instances, macOS enables scaling factors like 1.5x, where the final apparent resolution is 2560x1440, so that fonts are the same size as if it were a 110 PPI 27 inch monitor, but is using all the pixels of a 3840x2160 to display them.
These solutions are generally not quite as sharp as pure 1x or 2x scaling. But again, user opinions differ.
Note, using scaling like 1.5 x is the most taxing option for the GPU, because in an intermediate step, the final screen res is first rendered in a buffer at 2x the horizontal resolution (4x the number of pixels), and then scaled to the correct target resolution.
So for example, to display 2560x1440 on a 4K display, macOS first renders a 5120x2880 '2x' image, and then scales this down to 3840x2160. The result is a very nice looking image, but a lot of GPU calculations, which can make user interface animations like window resizing drop frames.
Summary:
1. If you want the fastest and smoothest user interface with integrated graphics and multiple displays, then choose standard 1x displays like 2560x1440 in 27 inch or 32 inch sizes (depending on what final font size you like), or 1920x1200 24 inch.
2. If you want retina quality font rendering and care about smooth UI, choose a 4K display and add more ram. Scaling should still be fine.
3. If you plan to run more than one 4K display, or also a 5K display, and maybe at scaled resolutions, then probably expect to need a dedicated eGPU: if you want really smooth user interface, then remember that each 4K or 5K display is equivalent to 4 displays that were considered quite large only 4-5 years ago. This is a lot of pixels to push around, so one can't expect miracles from the integrated graphics unfortunately. Having said that...reports indicate that the UHD630 actually works reasonably well!
