Well, it's obvious that a 2.5 year-old console isn't going to be able to pump out graphics as good as a high-end PC. I think the Xbox COULD run the game very well though, probably at least a consistant 30 FPS throughout the whole game, and they might even be able to add a 720p (1280x720) mode and still have it run smoothly, however I doubt that will happen because it's being ported by a company that is far from being skilled at porting games (Vicarious Visions, who also did the Jedi Outcast port). If ID spent a decent amount of time on the console, I think they could get some very nice graphics out of it, but it seems they have no intrest in doing that right now, so unfortunatly the Xbox version may turn out like Soldier of Fortune 2. Oh well, at least they aren't trying to port the game to PS2!
I guess MACs would be more efficient, but they will simply get trampled on by PCs due to raw speed. There's nothing availible for the MAC that can match up to a 4 ghz P4 with a 9800pro card, even though the CPU is much more efficient. Also with Doom 3 being locked at 60 ticks per second, there's going to be a certain point in CPU speed where a faster processor simply won't help. Though I forgot all about the MAC version of the game, since at this point MAC gaming is kinda dead...