Even the ones with the firmware that doesn't allow manual flashing are 1GHz, but showing single core activity in the firmware. All are C1 hardware, and I believe someone mentioned earlier receiving a C1 68U. I doubt Asus are shipping hardware that carries the same revision number but has different components.You have a different Revision, you can flash any FW manually right?
Anyway the BCM4708 is a dual core part. Can a core be disabled at the firmware or, boot loader level?