According to MaxConsole.net some of the new limited edition Halo 3 Xbox 360s are equipped with the long-awaited 65nm CPUs and GPUs:
News has come to light that some of the Halo 3 limited edition Xbox 360 consoles incorporate the 65nm CPU and GPU, which in essence make the console more reliable and less power hungry than the normal 90nm boxes which are to be found in every other Xbox 360 console released to date. We were all unsure when the 65nm consoles would hit, but it took us all by surprise that they have indeed debuted in the Halo 3 machines and not the Elite. However, finding out if you have the 65nm console isn't easy, as you need to take your console apart.
via Evil Avatar