Haddock, I do agree - the unstated assumption in my calculation was that AMD would have the foresite to allocate the pins of socket 754 wisely, so that socket 940 would be a superset of 754 (simply filling in the extra pins to permit two more HT channels). If the pins were designed such that some of the extra 754 pins are used by HT on Opteron, and some are used for dual DDR, then they would have to go to socket 940 for the high end A64 as the best solution.
I will give them the benefit of the doubt, until we know for certain. This means that I look at the fact 754 and 940 were spec'd and announced at the same time as evidence that they thought through this issue, and they worked out layout requirements to permit 754 to be dual DDR.
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