MacOS in particular gets amazingly slow when you don't use a 1:1 or 2:1 scaling. I too have have two 27" 4k screens and they made the machine unbearably slow. It got so bad that I now treat them as 1440p screens and let the screens do the scaling. It's not pretty and slightly hazy, but at least the machine is usable.

32” at 4k (native res, 1:1)

30” 2560-by-1600 (native res, 1:1) ( few monitors support this physically, but two are my goto: old 30” apple studio displays , and a 30” old dell monitor. Both can be found on eBay at very low cost , but do use 2 to 4x the power draw as modern monitors)

An option that I think might be interesting is 3 displays side by side, but with the center display in portrait mode rather than landscape mode giving overall an inverted T shape to your combined display space.

How does this work? Will it just upscale or is e.g. text still rendered at 4K? Rendering not at native resolution results always in blurred edges in my experience.