Why are you saying you have to scale to 1440p?
Mac display handling when running non-native for the display gets...confusing. Basically, retina displays use pixel doubling, e.g. combining 2 pixels in each dimension into 1, so a 3840x2160 display becomes a 'retina' 1920x1080p lookalike/effective resolution in terms of UI elements and font sizes, labels, etc....but 'crisper' due to the doubling.
The output to the display is still 'real 4K' as Apple scales the UI elements accordingly.
However, once you get to other resolutions that are not clean integer multiples, Apples does some 'weird things' in that it will basically double (possibly or more) the target resolution into a virtual buffer which is an even multiplier, then downscale to fit the screen target resolution. Someone else can probably do a better explanation, but most 4K screens amount to 'retina-like' in 1920x1080 'effective' resolution scaled, which for many, for text and other non-video-editing apps, isn't great (at least not for me).
The Studio or LG 5K works out a bit better at 5120x2880, which can be run native or in 'retina mode' of 2560x1440p.
For my personal use, 4Ks are nearly worthless, I just use a 3840x1600 at native resolution and give up the 'retina clarity'. My ideal would be something like a 40" ultra wide at 7680x3200 which I'd then consider running at 'retina scaled' 3840x1600. YMMV.
