I am a TASer, and I have been using the PAL version of lemmings for my MD/genesis TAS. The PAL version of lemmings actually runs 10% faster than NTSC on this console, whilst NTSC has a higher frame rate, the physics of the game updates every 3 frames in the PAL version, and updates every 4 frames in the NTSC version. So it would likely be best to use the PAL version for your runs. The PAL version is also a bit easier to find online (which is the reason I started using it back in 2017)

I wrote a bit more about it on the forum I write about my TAS in https://www.lemmingsforums.net/index.php?topic=2425.msg89912#new