Not to put too fine a point on it but ANYTHING running 6S will need near constant maintenance.

Think NHRA top fuel/funny car where the engines get opened up on an average of every 5~10 MINUTES of run time.

If you don't mind spending more time working than running then stick with 6S.

It's possible to build a stock traxxas diff that will hold up to as well as anything else to 6S but it's not something I can explain in a few paragraphs and requires a through working knowledge of how to properly remove any trace of backlash without binding anything up. If you really want to a badazz traxxas diff take a set of diff cups to your friendly neighborhood machine shop and get them to make you some press in inserts for the blind side of the cup. You will also need several different sizes of shims, some grease with a droop point of at least 500F, and the ability to feel the difference between no backlash and binding.