Classic (68K and PowerPC) Mac OS and Mac OS X are significantly different platforms. I am the admin for Pathways Into Darkness, for which the original game is on old world Mac OS, and a reimplementation, with version differences, exists for OS X. I got a submission for the OS X port and I'd like to be able to distinguish by platform from runs on the original game. I'd propose changing "Mac" to "Mac OS X" and adding "Classic Mac OS" as another platform, though that would mean current games run on Classic would have to manually fix their platform settings.
Marathon 2: Durandal (http://www.speedrun.com/Marathon_2_Durandal) is a PC/Mac game that has an Xbox Live Arcade port. Currently this is noted as having Mac and Xbox 360 checked for possible platforms. However, the XBLA port differs significantly from the original game (the engine is completely rewritten and runs at 60fps instead of 30), so I want runs of it to be in a different category. What's the "right" way to do this?