Sup peeps

Im putting together a new truck and the diffs are one of the components id like to beef up. Iv read the diff threads about peeps stripping the spider or ring gears. For some, shimming works for them. Others buy aluminum inner diff cups or aluminum outer housing.

My question is, what part of the stock revo diffs are the weakest links? (weak spider or ring gears, inner diff cup, outer diff housing, to much gear play?) and which one of these mods have the biggest impact on beefing the stock diffs?

Losi mod is out of the question so no need to bring it up please.