@dkazakov
I have just tried the latest build 17f2c8d and the WinTab setting as suggested. From a single display condition and Krita already started, after enabling a second display (Win+P, "Extend", to the right of the primary display) the canvas appears to maintain the correct tablet mapping, but from an extended desktop to a single display again ("PC Screen Only"), tablet-canvas mapping does not return to normal. In other words, this seems to work correctly only once, but it's already an improvement.

@dkazakov: I'm aware that the framerate is not "unlimited" anymore as in past versions of Krita, but I think the normal user expectation would be that when the update rate limit is set to 60 fps (for example) brush strokes should also consistently update at that rate.

@alvinhochun: I tried the indicated nightly build of Krita (4.0.0 pre-alpha git-465432e) and here brush strokes are painted as smoothly (i.e. with the same update rate) as with 3.3.2 official.

@poke1024: here are my observations.

The patch does seem to make a difference. I previously used (on Windows) an external program to measure the framerate in OpenGL/Direct3D applications, and it always showed a lower value than what was set in Krita. Additionally, the effective drawing framerate in Krita was visibly much lower than that.

I tried to apply the patch (using TortoiseGitMerge) on Krita-master from git, on Windows 10 64bit. I haven't measured the drawing framerate precisely yet, but compared to Krita 3.3.2 official, drawing still feels low fps-ish, even at the default 100 fps limit.

Practical usage considerations: if the "Temporarily save tweaks to presets" option is disabled, the displayed brush size for that preset will remain the last selected one until the preset is selected again; only then it will revert to the original size. Is this a desirable behavior? While at first it appears to contradict the "dirty preset" status/icon, it's consistent with the actual program behavior: if "Temporarily save..." is enabled after the size of a brush preset is changed and after selecting a new brush, but before selecting the previous brush again, the old size will appear to have been preserved. This means that brush size is reset only upon re-selecting the preset. The same occurs even after altering several brush presets.