I don't remember how fast turbo speed is on lix, but it's probable that even at that speed, it'd still be considered impractical to work through the 2^28 phyus needed to achieve fall distance overflow. At least not without modding lix to, say, do a version of turbo speed that truly runs as fast as hardware allows.
Frameskips would help here. NL has an advantage here: You can define an arbitrary length frameskip hotkey. If you wanted to, you could define a frameskip for 715827882 frames, which should be just enough to trigger the bug (maybe give or take one frame). Of course, it would still take ages to process. I opened Wimpy 28 "Get up, up, up!" from Lemmings Plus I, which is a very small level with few lemmings. I assigned a hotkey for 1,000,000 frames forward. It took about 1 minute 19 seconds to process this skip. That would mean nearly 16 hours to process the number of frameskips needed for the fall to become non-fatal. You
could assign such a hotkey and leave it running overnight - and you could use a PC that's more powerful than mine to save some time here too.
By comparison, Lix cannot (as far as I know) do arbitrary frameskips, so you'd need to be manually doing max-length skips repeatedly. You could perhaps write a script that does it instead. Lix also has high-resolution physics (NL offers high-resolution
graphics, but physics remain low-res, and so this has very little impact on the duration of the skip - the above test took an extra 3 seconds in high-res mode). On the flipside, Lix is much more efficient than NL at running physics updates,
and needs less updates before the overflow occurs. Still, I'm going to guess we'd be looking at
at least a few hours in the best case scenario, so this is pretty impractical for anything but the craziest of challenge solutions.
In either case, you could also custom-write a replay file that makes use of this without actually executing the solution yourself - but you've still got that wait to actually verify it. (Most likely, this will be quicker than actual in-game replaying on both engines. Not 100% sure for Lix, but NL does replay checks much faster than in-game replay playback, even when using frameskips.) And if it fails, you have no idea what actually went wrong, most likely.