Created attachment 643998 [details]
screen showing output of vbeinfo

i'm using an AMD GPU and a 2560x1440 native display.
on this configuration, the GRUB2 UI is slow to the point of unusability; it
takes a full second to flip from one menu item to another, 3-5s just to display
the boot menu, before booting starts.
drawing the chameleon logo is visible line-by-line, too

lowering the resolution helps, at 1280x960x32 the speed is almost usable,
1280x960x16 is sluggish but OK (so i'm sticking with this resolution for now)

my GPU is reported as follows:
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape
Verde XT [Radeon HD 7770/8760 / R7 250X]

detected graphics modes are attached