I thought I had better chime in here, just for Richardian continuity. I can't argue with the more experienced Richards who have commented above, but I run good ol' Castrol 20-50 GTX. More than one non-Richard on the forum advocates using really cheap oil that you change around every 250 miles (or was it 500?, I can't remember) because it is the stuff the oil picks up that causes engine damage and not the differences between grades.
Richard (L.)