If you have two monitors with very different DPI, for example, I almost poke my eyes out when I tried 5k and 1440p together, you only have two choices: render for 5k and scale down to 1440p or render at 1440p and upscale to 5k. Well, you can also pick a middle ground that makes both monitors look blurry. Either way, at least one monitor will be _very_ blurry.