--- Comment #4 from Jan Matejek firstname.lastname@example.org --- sorry, a correction. text does NOT appear instantly, but is rendered along with the border. (just confirmed this by switching to grub's edit mode. the screen is cleared and then a new border with the edit window is rendered, again, scanline-by-scanline)
(a clarification, when i say "line by line", i mean scanlines, as in individual pixels. not lines of text)
it very much looks as if a pre-filled 2560x1440 buffer is copied on screen and that takes a long time.
moving around and editing is responsive, which i guess is because a much smaller area is updated? it still feels sort of sluggish, but at this point i can't be sure whether there is a problem or whether my perception is wrong.