Best options for a budget display?

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This is a known issue. In quick summary, the macOS UI is designed for displays with about 110 pixels-per-inch. It looks good and is usable for a region around that (maybe 100…120 ppi). Or a display with double that (about 220 ppi, or the range of 200…240 ppi), which by default will give you the same size content, with 2:1 “retina” image scaling. (FWIW, I use s 24" 1280p display, whose resolution is about 97 ppi. It looks great to me.)

But a 27" 4K display is none of the above - it will be around 160 ppi. Which means everything will be too small without scaling, or will be too large with 2:1 scaling. In order to get it to a comfortable size, you need to run it at the equivalent of a 1440p display - an effective resolution of about 110 ppi. Which you can and probably should do.

The problem is that scaling 1440p up to 4K is a non-integer scale factor. Internally, macOS is going to render your content at double-size (2:1 scaling) to a 2880p (aka “5K”) frame buffer and then use the GPU to scale that buffer down to your display’s 4K input resolution. The result is a great looking image, but one that uses a not-insignificant amount of GPU power - power that isn’t needed for images with 2:1 scaling (1080p equivalent) or with no scaling (4K).

If you’re not running GPU-intensive apps, this may not matter - you’ve got the horsepower to spare, so go ahead and use it. But if you are (see Hunter King’s video, below, where he talks about it impacting his video rendering performance), then that is going to adversely impact the performance of those apps. If this is your typical usage (as it is for Hunter), you may want to instead buy a 27" 1440p display. You can run this without any scaling, gaining back all that GPU power for your apps. You’ll get the same size image, with almost the same quality, but without the GPU doing any powerful scaling.

It’s worth noting that all of Apple’s desktop displays are designed with this in mind:

All of these mean that with the default 2:1 scaling, you get an effective 109 ppi, which is precisely the resolution around which the UI was designed.

But it’s interesting to note that their laptop displays don’t fit this pattern:

These, with 2:1 scaling produce a UI with an effective 127 and 112 ppi, respectively. The Air’s resolution is still within that sweet spot, but the Pro is slightly higher resolution. I assume that Apple considers this OK because users typically sit closer to laptop screens than they do to desktop screens, so slightly-smaller UI elements won’t be a problem.

See also:

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