So I now race mainly touring cars, and I also race with one of the fussiest gets on earth (but then he's done ok for it!!). His view is that schumacher have the best diffs in the business, bar none. The design is the same, so there is no theoretical reason for the off rd ones to be any different - unless there is somehow issues with outdrives. Every other touring car manufacture HAS to run gear diffs, we have a choice.
Anyway, as far as components go, the U1954 thrust race is IMHO the best item in the business - and I know other on road teams that have used them in the past
It's not listed in the off rd section for some reason, but it's the only one that I would use.
Diff balls, I'm not sure. Generally i'd say the ceramics - but actually, there is something in me that things Tungsten carbide might actually be better for an off rd diff. They are a little more robust - and generally I used to find that they didn't always need quite as much tension to grip as Ceramic.