@Ian
There is no 65nm GPU for the XBOX 360 yet.
All HDMI XBOX 360s are either 'Zephyr' motherboard (as first seen in the Elite) with 90nm CPU and GPU, or the 'Falcon' motherboard (with 65nm CPU and 90nm GPU, as seen in newer Elites and Premium/Pros, and most probably in the new Arcade).
The 65nm GPU boards ('Jasper') are not due out until August 2008:
http://www.reghardware.co.uk/2007/10/11/ms_readies_jasper_xbox/