The fact that Apple legal is on the move seems to support the theory that these specs are real.
One user in the forum kps linked to stated a very good point (at least in my eyes):
"What has Apple been working on for the last 2 years while the G4 stagnated in speed and irrelevant spec tweaking?"
I think these specs could very well be real. 8 GB RAM seems to be an incredibly high number, but Apple has been a pioneer in lots of things in the computer industries.
And the fact that there are no PCI-X cards available at the moment doesn't mean that Apple wouldn't put it in their PowerMacs. Remember USB? It was not before the release of iMac that it became hugely successful (when the iMac was released there was hardly any USB hardware available).
Looking forward to Monday!