Motorola MPC7457 Information (PDF)
Motorola has posted a PDF with details of the MPC7457 processor.
The MPC7457 is described as the fourth implementation of the G4 Processor. It's a 32-bit chip with a 512KB L2 cache (2x that of previous chips), and support for 1MB or 2MB of L3 cache.
According to the July, 2003 Motorola document, MPC7457 processors will be coming in at 867MHz, 1.0GHz, and 1.3GHz, with bus frequencies up to 167MHz. This is contrary to previous notes from The Register and Motorola documentation (PDF) that the chip would support a 200MHz bus.
Current Powerbooks sport 133-167MHz buses. Speculation has placed the PPC7457 in the long-awaited Powerbook revisions... but no significant confirmation of this is available.