I'm brand new to this forum (although not to Myth 2 ) - looks like a great spot.
Anyway, I am having trouble with the 1.6 version. I am running Intel OS X and I can't find the key that changes the game speed. I remember being able to go up to 16x or something...
I would imagine it would be the same for you, but for me... I'm on Windows and it is F1 to slow down and F2 to speed up. This only works for single player of course.
If you're on a Mac laptop, chances are you need to hold the Fn key while pressing F1/F2 (or other function keys), as otherwise the function keys are used for other things (ie: brightness control).