when you flashed the bios to a new version, it probably started at "optimal settings," which in your case, seems to include as a default setting a cpu throttling feature to lower frequencies during non-load (as the others have stated prior to my post). depending on the bios, whenever you flash, you will have to go back into the bios and reset all of your specific settings back to what they were set at before the bios flash. (my bios, for instance, gives me the option when flashing to erase everything or only update specific items while leaving my changed settings intact).
Hmmm...
The thing is, I'm a big chicken when it comes to BIOS, I only change basic stuff like... Memory timings, Boot order, etc...
I would never mess up with something like 'CPU throttle'.
I'm even scared of disabling AMD's 'Cool n Quiet' feature lolz.
It has to be something new that ASUS wanted to incorporate into their new BIOSes.
EDIT: Thanks BTW.