Wow! My manners are horrid! I just logged on for the first time since posting my RFI - I was expecting an email alert if anyone replied, and thought no one had done so. Thank you all so much for your comments.
As of yesterday, I had decided to bite the bullet and tackle that G5 2 or 2.5 GHz machine, although I'm quaking at the sticker. Having read your various posts, however, I'm finding my commitment wavering. Speed does matter to me, and I do plan on working in 3D. Who really wants to spend 3K if it's not absolutely necc.? (Course, I'd get one of those really pretty screens, too. +1.5K+++)
I'll post my final decision when I've made it. Thank you all again.