Since you have a non-ES CPU I believe you'd get multiplier locked out when applying BSEL pinmod. Could be wrong. Could always revert to a FSLx PLL pinmod to get a 266Mhz FSB. Has been done on a 965PM chipset successfully. Likely running a 2.8Ghz CPU at 4.2Ghz as you are now is the the edge of cpu stability unless you have some crazy good cooling. Only advantage of increasing from 200->266Mhz FSB would provide faster RAM/video response with CPU multiplier pulled back to x15/x16 (4Ghz/4.27Ghz) from the current x21 to provide CPU stability. Is it worth the trouble? 4.2Ghz@200Mhz FSB is pretty impressive, if stable.