Thanks for the helpful replies.
honold, I'd certainly be interested in any unclocking bench comparisons you'd be interested in making. I'm pretty naive on various benchmarks...I'm more interested in office and web benchmarks than anything else.
Woody, as stated in OP, it's a 800mhz FSB. I neglected to mention it's a 2.4C, if that makes any difference.
I didn't realize asynchronous mode introduced extra overhead. I'd guessed that 266, as 1/3 of 800, (vs. the 400 which is 1/2 of 800) might be a nice multiple, and should play pretty well with the setup.
Thanks for taking the time to write such a detailed post!