MacCentral posted preliminary benchmarks from the new PowerBook G4's which were released on Jan 31st.
The site provides a small chart running various benchmarks including SpeedMark, Cinema4D, iMovie HD Render, iTunes encode, Photoshop, Unreal Tournament and Compress MPEG2 encode.
Overall speeds are only slightly (as expected) better on the 1.67GHz vs the 1.5GHz machines with the exception of the Compressor MPEG2 encode which was fastest on a 1.5GHz model for unclear reasons.