first of all, i don't think 775 will phase out anytime soon. i7 just hit the market and i'm sure the average person does not even know what i7 is.

anyways, it looks like your results are pretty good with 500+ fsb. i haven't tried every x48 or p45 out there, but from the maximus II that i have, reaching 500fsb on a quad requires a bit of tuning. comparing it to the same ROG family, the rampage extreme seems to do better even though the chipset is 90nm compared to p45 65nm. someone correct me if i'm wrong on these two comparison. now this is also just comparing two specific mobos within the same company, but i'm sure you're right that generally p45 will clock higher than x48 when looking at a wide range of other mobos.