NTSC being 60Hz and PAL being 50Hz, there is compensation implemented in code such as shorter autorepeat delay (16 to 12 frames) and rate (6 to 4 frames), as well as gravity drop speed past level 10 (-1 frame) to keep the gameplay sort of similar to casual players.
But then details matter at these insane player levels, NTSC is 1 row every 2 frames on levels 19 to 28 then 1 frame starting with 29, but PAL is 1 row every 1 frame ever since 19, so given that frames are not the same duration PAL is comparatively harder than NTSC starting with 19 but easier starting with 29 (... provided one can survive up to that).
So wall-clock PAL gravity ends up being 1.25x faster than NTSC (but with quicker DAS: 1.5x faster delay, 1.33x faster movement), then at 19+ is 1.67x faster, then at 29+ 0.8x "faster".
But then details matter at these insane player levels, NTSC is 1 row every 2 frames on levels 19 to 28 then 1 frame starting with 29, but PAL is 1 row every 1 frame ever since 19, so given that frames are not the same duration PAL is comparatively harder than NTSC starting with 19 but easier starting with 29 (... provided one can survive up to that).
So wall-clock PAL gravity ends up being 1.25x faster than NTSC (but with quicker DAS: 1.5x faster delay, 1.33x faster movement), then at 19+ is 1.67x faster, then at 29+ 0.8x "faster".