So I've done an upgrade to the latest FreeBSD 7.2 amd64 code on the server. In addition I've cleaned out a lot of dust clogging a fan or two and swapped out a 10/100 Intel network card for a 10/100/1000 Buffalo network card (Realtek based). Overpaid on the Buffalo card as I found it cheaper down in Quarry Bay than at the Wan Chai Computer Center.
I found a cheapish TP-Link 5 port desktop gigabit switch at the Hong Kong Computer Expo, so I'm finally taking advantage of the Gigabit port on this old Mac G4. And it speeds up transferring large files between the Mac and the server.
On the lookout in HK for a source for this TP-Link gigabit PCI-Express NIC with a comparable price.