1am
After an hour or so asleep, my head went "Hey, I wonder if changing x-line a bit would help speed the engine up at all?"

-=-=-

The command "LET" isn't used from the frontend, but it is in fact used by the parser, to specify the difference between a standard variable, and you setting one.
It all gets significantly messier from there, but indeed, that command does take centre stage.

I did a bit of tweaking to how this "LET" is recognised, and also rewrote a chunk of the variable code, compressing it down and squeezing as much "fluff" out of the code as I could.
As has been the standard of late, I've just about managed to get a few extra milliseconds out of my test script.
Gud gud!

I also added variable handling to the "quick check" section of the code, which appears to have helped a bit, but I'm also wary that adding too much stuff up there will end up bogging it back down again, so I'm being extra careful how much I put into that bit.
Hmm.

By around 4am, I was ready to try and get back to sleep.

Today I'll finish off last night's tweaking and double-check I didn't break anything else along the way!