I give up! You guys are posting faster than I can keep up with, and rendering my next post irrelevant before I can submit it. My previous post was being written when FromWithin posted his. I feel like I'm in a "Back to the Future" movie here.
I guess I can't argue with the recollection of a Bungie developer, but I can say for sure that it contradicts what was being reported in the game magazines at the time. One magazine was suggesting that users upgrade to 800 MHZ CPU's to get the most from the game, and that was before the buyout. Since the initial X-Box spec didn't exceed that (unless I'm once again mistaken), I can't explain the apparent conflict.