You guys are probably already aware of this since it appears to have been written by someone on the project team (Alex) - but the online gaming magazine/site "Gamasutra" just published an article about Magma's 1.5 and 1.5.1 updates to Myth 2.
"However, one of our internal testers was using Mac OS X 10.1, and for that individual that change gave a huge FPS drop (by about 6 fold), so we had to revert and put that extension back into use."
Holy cow. The difficulties you had with different OSes and graphics subsystems reads alot like the TFL postmortem. No wonder the folks at Bungie were happy switch back to a single platform.