i ran the amsoil. also ran there synthetic race oil. switched back to Torco for the gear cases and Brad Penn for the engine. mostly cause of pricing, seocd found no performance gain either way. so if you change oil often, i couldn't justify the added cost - almost 50% more for Amsoil.
also the Torco is not a full synthetic compared to Amsoil. I've also noticed here in Florida with high humidity that 100% synthetic products seem to be adversely affected by the humidity.
i've also run Fina's gear oil meeting the same specs with no issues and costs less than half the torco.