The only reason to get a G5 these days is if you need to run classic mode applications or PPC applications. Other than that, the Xeon is much better. The G5 would be holding you back in virtually every way.
I'd go so far as to say that for "classic"(i.e. OS 9) applications, you're better off with a high end G4-specifically a single or dual 1.25 MDD(not FW800). In my experience, not even a high-end G5 can run OS 9 programs as well as running them natively in OS 9.
As far as OS X native PPC-only applications, though, it is hard to beat a high end G5.
I use a dual core 2.0 G5 daily, but don't do anything strenuous on it. Actually, it's been out of commission for a week or two, as I borrowed some parts from it(air deflector and hard drives) to get my G5 Quad working at home. I've been using a Macbook Pro for everything at work.
I'm currently shopping for a Mac Pro to replace it.
I love PPC Macs(a check of my posting history will show that it's the forum where I'm most active, and it wouldn't be too hard to turn up a list of how many I have-it's over 60 at this point). I do what I can to keep using them, but for many things an Intel Mac is just better.