"you'd never really see processors over 4GHz."
IBM released a 5GHz POWER processor 2.5 years ago: http://www.theregister.co.uk/2008/04/08/ibm_595_water/
IBM released a 5GHz POWER processor 2.5 years ago: http://www.theregister.co.uk/2008/04/08/ibm_595_water/