In my experience with my big and heavy extended savage aluminum diff cups, with shims and 4 gear diff takes care of the problem. My savage wouldnt handle my axial .32 I ran in it for two years without the upgrades.

I now have been running my savage with a 7XL and 4s and sometimes 5s lipo and the diffs are holding up fine even with the slipper tighten all the way with a metal spur gear. In two years of racing and bashing I only blew the front diff out once with my setup, and that was because I had the throttle pegged and ran into a nasty wall at high speeds. Gotta let go of the throttle when your going to run your front wheel into something hard & fast