1.2GHz G4s

Spymac reports that the 1.5GHz claims may be unrealistic:

"[At this point] don't expect anything much higher than 1.2GHz."

It should be noted that over the past few updates, G4 Mhz has only increased by 133mhz in each 6 month time-frame. To expect 50% pure-MHz jumps would be very optimisitic.