The NB, or MCH if you prefer, has to be set to specific speeds and latencies. With a 1066mhz FSB CPU the NB strap is set to 1066mhz and a certain set of latencies. A higher (faster) strap will allow the chipset to run faster but also to run at higher latencies. As you OC faster and faster, eventually your NB will not be able to run at a given strap setting so you may benefit from setting a higher strap. Several MOBOs have recently had bios updates allowing a 1333 strap for higher OCing with current 1066 FSB CPUs and likely for future compatibilitywith 1333mhz FSB CPUs.