This might be the only "General Gaming" board in existence where the fact we have the game memorized enough to answer immediately isn't surprising

.
Rama said he's on an iMac, and since he can play original, uncarbonized Marathon, he must not be on an Intel iMac. Accordingly, I still recommend the PPC/NIBs version of Aleph One. I've been keeping track of what the Universal/SDL version can do, and while it's getting better, I still think NIBs has advantages.
The high-res textures are great, no doubt about it. I've been working on the Aleph One version of the
E:MR mod, and while re-doing an entire monster class would take a ton of work, I've been slipping in high-res sprites here and there. Even though it's a 2.5D, sprite-based engine, it can still look beautiful with high-res graphics.