The voltage regulators Asus uses are not known for thier stability. If your update affects voltage regulation, it may help with OCing.
I think that your chip may need a little more time, and voltage to get to 2.5. My venice 3200 couldn't get to 2.5 till it had been running for over 3 months. It does that now @ 1.475, but needed 1.5 at first.