Actually, there is the 1.7GHz Freescale 7448 (specifically part #KMC7448VU1700LD for an Rohs version).
But Matt's technically correct as this isn't a G4. Rather, it's a drop-in pin for pin compatible chip. Or as Freescale puts it "The e600 core is virtually identical to the G4 core, but with enhancements to L2 cache and AltiVec implementation, and it is manufactured in 90nm technology. Software written for the MPC7447 and MPC7447A will run seamlessly on the MPC7448. MPC7448 can be a pin-for-pin compatible drop-in replacement for MPC7447A".
So, with a larger cache, improved graphics related instructions, Rohs compatibility, and the ability to directly replace a G4 this would be faster than a 1.5 GHz G4 (or any of the Peg2 processors).

[ Edited by Jim on 2009/2/21 0:58 ]