PAL is definitely slower. PAL will always be slower as it runs at 25/50 FPS unlike NTSC which runs 30/60 FPS.
NTSC-J 1.0 and 1.1 are faster for speedrunning because there is slightly reduced lag spots, like when the train is on screen in Kalimari Desert.
NTSC-J and NTSC-U have version differences where some skips don't work on one version, but do on another. To use the current WR strats abney317 uses, you need to use NTSC-J 1.1.
How to tell what version NTSC-J you have? Turn the cartridge over and look at the backside. If it says "NUS-JPN" in the lower right corner, you have 1.0. If it says "NUS-JPN-1", then you have 1.1.
There are some interesting things to read about MK64 in the links provided below: http://tasvideos.org/GameResources/N64/MarioKart64.html https://tcrf.net/Mario_Kart_64
Did you know there's another music loop for the "Winning Results" part, but only after the one you normally hear loops 64 times (54 minutes and 39 seconds)? You can listen/read about this and many more fun things in the links provided above.
