Roger, I use a small amount of standard diff grease on both the thrust bearings in the Schumacher diff and it's fine. As you say, you need the right grease for the right application, so I would venture to suggest that the perfect solution would be silicon diff grease on the spur gear (where all that's needed to to help the balls rotate freely in the holes) and some form of high pressure grease on the thrust race in the hub - some EP version perhaps?
Just thought my experience might help in making choices for Frost...
