for the desert rear's:
The desert is very hard and made for powerfull bikes at extended speed but no longer produced, get them if you can. I love it on the 950 for dry/desert ground.
The desert race has a lot lower profile and is made from softer rubber. specifically made for the 450's now active in dakar. Ive seen it wear a lot faster on these bikes than the old desert, grip is better on rock's and sand. I think on the big bike this is not your best option if you'r looking for a tire that you wont replace after every day racing for a new one.
999 LC8 Rat-Rally custom - 500 EXC - XR666R '85