In my experiments the past two weeks, what I have seen is that as you raise the FSB at the processor, you need to bump up the Vcore a little bit more than the pure speed would imply. While I can run 11.5x200 at 1.75Vcore, everything else remaining the same, at 11x210, it takes 1.775 for truly stable operation. At 10x230 it took me 1.80Vcore for the same stability. It's probably not outside what is to be expected. These results are anecdotal to my particular hardware compliment and it is probably different for someone else. At the upper end of what is achievable, nuances become critical factors.
Hoot