> My Powermac does not weigh 44 pounds.

The PowerMac G4 MDD/FW800 weighs 42 pounds (= 19.1 kg). Your Quicksilver would be 30 pounds (= 13.6 kg).

http://en.wikipedia.org/wiki/Power_Mac_G4

> is the G5 going to weigh that much less?

PowerMac G5 weighs between 36 and 48.8 pounds (16.4 to 22.1 kg).

http://en.wikipedia.org/wiki/Power_Mac_G5

> as far as anyone knows, there hasn't been any word
> on 7447 or 7448 upgrades

As I told you several times already, there have been words on 7448 upgrades. I'm not going to give you the link again, though ;-)