Strap 400 is slightly broken when @ higher HSB IMO...
For my case, 600FSB boot will quickly freeze up using 400Mhz Strap, which will never happen in 333/266 strap.
So I guess for higher FSB you may need to stick on 333 Strap until a patch for BIOS is up in order to fix this problem.
BTW one of the wierd thing is, when high FSB (i.e. 600+ for duals, 450+ for Quads), when attempting to save and exit the BIOS screen will freeze instantly that need hard reboot to make new options to take effect. Anyone experienced this issue?