Seeing that there's no price difference (almost) between 667 and 800 MHz FB-DIMMs, I'm thinking to order 800 MHz ones for my first generation Mac Pro. No, I don't think there's going to be a performance difference, it's just that they are useful in a Harpertown Mac Pro too (should I get one some day). Has anyone done this so far? Barefeats says 800 MHz modules work just fine in first generation Mac Pros.