Actually, I just realized the G5 I grabbed was one with a radeon 9800. So it was the GPU. However, for testing I dropped Rez down to 2400 x 600 (3 - 800x600) an I am noticing some pretty significant overhead.
One file DV NTSC and this is what I've got:
Graphics - 90% to 140%
Timing - 100% to 150%
This seems odd to me. Like I said, 1 DV file running only.