The Intel processors are way faster than the PowerPC processors. (Unfortunately; I really like(d) the PowerPC architecture.)

I would venture that any Intel-based Mac is going to be faster than any PowerPC-based Mac for most things. Given that the cheap G5s you're looking at are likely to be single-CPU and the new Mini has a Core Duo (effectively two CPUs), I can't imagine that the raw processing power would be more with the G5.

That said, the video processing on the G5 is likely to be a little better. But you're not exactly running Quake doing video editing, so I'm not sure how relevant that is.

I'd still probably choose the Mini, unless the G5 is multi-CPU and has significantly more memory.