I have a 2560x monitor, and I’d guess that this is the worst resolution for Renoise - (say 27" and below). That’s something to bear in mind when investing in a new monitor.
With 4k, you could at least run Renoise in “double pixel” mode (200%) - 1920x1080, which seems pretty optimal to me. Or 100% if the monitor is of the big ass type. I’d imagine it works fairly well with 4k (?), at least compared to 2560.
PS. The Renoise dev has said that they started working on a high DPI GUI.