It's not just that for PAL vs. NTSC as many games are programmed to wait for the vsync & re-programmed for the regional variation.
Which one of those affects the speed of the gameplay? Very few, on the face of it. For manually-timed tracks, the use of a drive emulator should disqualify the run as it will likely give a speed advantage over original hardware. In various ways the rest only change the experience and/or accessibility of the games. However, replacing the oscillator with a faster (or slower one) as in the PAL/NTSC you describe, will likely adjust the speed of gameplay. As the scoreboard performs the split to ensure comparing like-for-like performances, a 50Hz PAL console with an NTSC-speed rated components is invalid. It's a console which was never designed to run at NTSC-equivalents & theefore is no longer "original".
However, a PAL console which is both 50Hz and ~60Hz capable (PAL-region Dreamcast, PS1, PS2, Xbox and many others) as produced by the manufacturer is capable of NTSC rated speeds where the console and game combination boots as NTSC/PAL-60/PAL-M (all of which are ~60Hz outputs). (I don't believe there's an NTSC equivalent console but just in case: an original manufacturer NTSC console capable of both ~60Hz and 50Hz speeds would be accepted as PAL given the parameters of the performance).