THIS COULD BRICK YOUR BOARD! OVERCLOCKING IS A HACK NOT A FEATURE!
---> found here: https://gist.github.com/bnewbold/407140
--> only overVOLTAGE can harm your board
I do overclock my pic32mx250 every time from 40mhz to 48mhz, because I'm lazy
---> 48mhz = USB clock and a odd audio frequency for I2s.
So 128MHZ should be possible. Here at Vienna we have about 38 centigrade, perfect temperature to stress overclocked board in the sun.
don't forget to change the system clock define (720000) in stm32.h or somewhere else (can't remember) or your peripherals run mad.edit:
an yes, Roger warned about USB