Well, i made a couple of tests in order to understand at which rate my DS1074Z refreshes the lcd screen panel waveform section content, what i found seems to confirm what i was thinking, i have around 20 FPS @ 5ns - 12K setting.
First one : i recorded some short movies of the screen with my panasonic SD700 @ 1920x1080 50p, so i converted them in a png sequences then i visually checked every frame, there is one actual screen update about every 2 movie frames.
Second one (unscientific & subjective) : i built some animated GIFs with sequences of screen captures (made with RigolBildschirmkopie) at difference frame rate, the ones that more replicate the real screen scope "experience" are around 20-25 FPS.
It should be necessary a faster video recorder for an accurate measurement but i do not own one, anyway i feel that those number are quite correct.
In attachment an animeted GIF @ 25 frame per second, visually quite similar to what i see on the scope screen refresh rate wise, obviously its content is not correct due to skipped frames.