I'd recommend that you go with CJ-4 Rotella 10w-30 or 15w-40 if you have to use something thicker. The other oil I'd consider for a shearing monster is that "secret" oil, that, if I'm correct, Terry Dyson formulated for Renewable Lubricants Bio-Synthetic. Some of the RS4 guys are using it with great results and their motors absolutely destroyed reputable oils.