Slow GUI on MAC with external 4k display when res is scaled

[schnesim]

I'm using a Macbook Pro 15 Mid 2014 running Sierra and a Windows 7 guest.

The GUI performance (dragging a window, scrolling) is unusable slow when the external screen is running a resolution lower than it's native one. So e.g. if the resolution is set scaled to 1920x1080 the guest is slow, if I change the resolution to its native 3840x2160 everything is super smooth. The issue does not occur at allwhen I move the guest window to the built in screen of the Macbook.

[NotMarcet]

I'm having the same problem with an external monitor on my iMac. It's smooth on my retina main screen at full resolution, but very slow on the external monitor running lower resolution.

[d4884]

Another user experiencing this issue. Would love any workarounds. I'm using a 2016 Macbook Pro connected to Apple's LG Ultrafine 4K display. UI is nearly unusable and will often spike the CPU when Virtual box is on the external display. Virtual Machine is WIndows 7.

I tried the original poster's idea of changing the external display to native, but at least on High Sierra with the LG display, that's not an available option - I believe it's using its native resolution already and the problem still manifests.