Yeah, I have had My G3´s for more then a year now, and I have charged them with 4C almost everytime and they are still performing good. Nice, that will give it a real "try out". "We'll see. I ran Summit shafts in the middle before" So.. aren´t you running summit shafts in the middle now?
How about the traxxas steel centers? Is it that simple that you just don´t like them for some reason or is it because you have to drill them up to make them fit on the diff´s outputs?
You could use a Rc monster cup on the diff side...No drilling required.. Since they are dogbone looking on one side:
http://www3.towerhobbies.com/cgi-bin...?&I=LXYCU2&P=7