ThinkSecret provides some more details on PowerMac G5 Updates.
According to the rumor site, the new machines should arrive in dual 2.5GHz, 2GHz and 1.8GHz models as well as an entry level single processor 1.8GHz model. ATI 9600 XT and NVidia GeForce FX 5200 Ultra graphics cards are to be offered.
ThinkSecret had warned that the bumps could be pushed back later this week. Indeed, one MacRumors source has indicated that the update may have been pushed back just one day at the last minute.
The release day apparently remains a moving target.