Theory about reducing multi-display idle clocks

[ToastyX]

No, the answer is the memory clock can't change if the vertical blanking is too low because there won't be enough time between refreshes to retrain the memory without visible screen corruption, but that's when dealing with a single monitor. If you have multiple monitors, all of the monitors must be perfectly synchronized so the vertical blanking happens at the same time on all of the monitors, otherwise it's impossible to change the memory clock without affecting at least one of the screens. In theory, if you change the UHD monitor to use "Automatic (HDTV)" timing for 3840x2160 @ 60 Hz, then it should be perfectly synchronized with 1920x1080 @ 60 Hz (the pixel clock will be exactly 4x), but I don't know if the driver will handle cases where the resolutions don't match exactly, so there's probably no way to make this work. The resolutions already have enough vertical blanking time, so changing that won't make a difference.