I think we should have different game verions. The DOS version runs with different speeds then the Steam version. Alsso the Steam version isnt the original one, it is a remake so can be counted as a diffeent game :D

I kinda agree with this, sorry for being two years late with this reply, as the DOS version sure runs different. But would that make too much effort, as this webpage only has on supaplex page, (almost) all the runs are done with steam remake of the game, yet it still shows up as the original 1991 version?

I did a few measurements and running supaplex steam version is about 10% / 15% slower on my machine than original over dosbox. So it seems that for single level runs using original supaplex will lead to faster times. What are the rules on emulators like dosbox by the way, is it allowed? Any requirement for configuration such as dosbox cpu cycles, etc? Some of those settings affect game speed to different degrees.