i think it's just feel,not true
cause u use E2 with 624mhz for a long times,it mean u were acquainted with that speed,so u didn't recognize difference between 318mhz and 624mhz
example,at now u sample downclock 318mhz,and then u use it for 1 week,afterthat u overclock 624mhz again.u'll feel faster more_of course
(but cpu's speed before u downclock and cpu's speed when u overclock again are the same)
i'm not sure , i've just guess
sorry my bad Eng,so i couldn't describe my idea more clearly
if i said smething wrong,plss forgive me