The core frequency of the CPU is not going to be where the interferance will be. It will be the bus speed. This is limited if the designer has good grounding and signal transmission practices on the board. I would actually expect more noise from the switcher in the power supply. That was where most of the 370 era computer room "noise" came from. That was what most folks didn't understand when they were doing all that bonding. The thing they were protecting the computer from was the computer itself.
