According to the DayStar site, the 12" upgrade only went up to 1.67GHz and the 17" to 1.83GHz. However, the 15" could be upgraded all the way to 2.0GHz!
http://daystartechnology.com/Apple_Mac_Products/XLR8_Macintosh_Products/Mac_CPU_G4_Upgrade_PowerBook_AL_PS.html