I have to be honest and say that hearing C3PO's voice that low, is much of a change, and kind of weird at first. If you intend to keep it, I suggest definitely adding an English subtitle track to the full length film, just to make sure, because I didn't quite understand his dialogue.

Anakin's voice change is very good though. That's sure to keep him from sounding even less like a whiny girl at some points. The scene where he confesses to Padmé having killed the Tusken camp comes to mind. That one should definitely benefit from it.