remowilliams wrote on 01.02.09 at 22:54:18:

on my MSTE (regardless of 50hz/60hz) it is running insanely fast. I just verified Captain Fizz behaves correctly (the same as STeem) on my 1040ST.No flickers, sane music and correct game speed at 8Mhz.

So, it's NOT NTSC.

I would say your MSTE has issues waiting for vsync for some reason. What TOS version is it?  We've tested on MSTE on TOS 2.03 and 2.04, but obviously cannot test on NTSC TOS systems.