I would go with any good synthetic that is approved for limited slip differentials. I don't know if you ever have it out in the Colorado cold but I think it would be better for that.

I know that my race car would always run a tenth slower on the first run of the day until we switched to a synthetic rear end oil. After that the first run was as good as the second. I have seen others that have had the same experience.

However I run a spool and don't have to worry about taking car of the clutches etc.