Well I have used for years Rotella T Synthetic from Shell Oil (Wally Mart @ $20.00 / gal approx) -- 5W40 and have no worries at all. 0 weight or 5 weight -- come on!! -- pretty thin stuff and 40 weight with the engine up to temp and or in the summer -- seems about right.
Mobile 1 is good stuff and fine if money no object for oil changes and or if you are paranoid about a mfg recommendation and who knows what "deal" is behind all that !!