Well, if I was keenly interested on making sure I was hitting the absolute top-end FSB overclock, I'd consider my options, but in truth, I don't care that much. To me, 500MHz is a sweet spot, and I know that the E8400 can handle it. The best chance of a higher FSB would occur with the Dual-Core I'm using, and I certainly don't plan on changing it (since I bought this one).
I just don't think it's worth the time and hassle of finding another chip that overclocks higher, since as I mentioned, the people who truly care about those results are in the minority, and because of that, it's not a huge priority. As long as a board hits 500MHz, I'm pleased with it. I do know that the E8400 can handle upwards of at least 525MHz, but I haven't seen that stable yet, on any board.