350 and above PII's run at a bus of 100Mhz (not quite sure about 350's but definetly 400's and up) I definetly agree with the do not turn down bus speed rule because it may not slow down CPU speed but it will slow down EVERYTHING else in your comp. Always start with and end up with either the same bus speed or higher, i wouldnt recommend sacrificing bus speed for CPU when u consider the consequences.