Not a solution but a TECH POST
Decided to look into the difference between NTSC and PAL. We've been using PAL due to the ROM being more easily accessible back when this started, but most speedruns tend to use NTSC and this port was made in an NTSC region, so I wanted to see if there was a big difference.
The PAL version updates everything every 3 frames, whilst the NTSC version updates everything every 4 frames, so played at the same framerate, the NTSC version is 25% slower than the PAL version.
PAL megadrive has framerate of 49.70146, whilst NTSC genesis has framerate of 59.92275, so running the same thing, NTSC is about 20% faster than PAL
Putting this together, the NTSC version should be 10% slower than the PAL version
I did an experiment to check:
Loaded FUN 8, made an input on first frame that the first lemming falls off the platform.
In NTSC, this took 1364 frames, so ~22.76 seconds
In PAL this took 1028 frames, so ~20.68 seconds
1028/1364 = ~0,75
20.68/22.76 = ~0.9
So my predictions work out
Therefor the we should continue using the PAL version because it's faster
The only thing that does move faster during NTSC gameplay is the cursor since that isn't bound by the physics update cycle
---EDIT
I changed the table on the first post to be more accessible to people not as familiar with frames.
And here's tricky 20 in 55.49 seconds (2758 frames)
https://www.youtube.com/watch?v=A_Klq91ybCELoads of lemmings here which means its a "don't look directly at the lemmings" level, oh well. Goes under the one way wall as you'd probably expect.
---EDIT2
Tricky 21 in 52.68 seconds (2618 frames)
https://www.youtube.com/watch?t=38&v=vl5KFDKZEYoThis one features a newly discovered (I think) glitch seen at around 0:38 where a bomber instantly explodes, skipping the oh-no state, due to being caught in a trap at the same time. A bit of a messy and hard to optimise level, I'm sure a few more seconds can be saved here.