IMG, a Mac Games mag has an interview up with John Carmack discussing programming on the Macs, gaming performance, the new G4 and what the "base iMac" should be (64MB RAM, Rage128 Vid Card, better speakers and a better mouse. Here's a quote:

Bernier: Why do fast Macs (B&W G3), even though they often beat Pentium machines in Photoshop head-to-head, trail behind PC machines in 3D games? Carmack: Photoshop filters are excellent optimization testbeds, but they are rarely apples to apples comparisons because of their hand tuned nature. I'm pretty sure that if Intel put some of their top guys on the task, they could be competitive with PPC on most Photoshop filters. There are certain tasks that AltiVec can be much better at, but in general, the raw computational rates are pretty close.