Does using an EXE patch rather than an effect to adjust the speed allow the creature to respond correctly to haste, slow, etc.? If so, could a similar patch be applied to player characters to recreate the BG1 walking speed when playing BGT or Tutu?
Got there before me. As a quick sanity check, it might be worth firing up a hex editor and scouring the EXE for each variable name before you delete it. We know PST has a lot of hardcoded shit, and I imagine embedding variable dependencies in the binary is not beyond it.