It’s really difficult to discuss these 2 formulations, as neither has a product data sheet with finished oil specifications to compare.
And I think the real problem, here, is that the oil inside the bottle is being judged with the “marketing terms” on the outside label.
Both MC 5W-20 & Walmart Supertech 5W-30 have the “synthetic” term on the label, since anywhere from a significant portion to over 85% of the base oil content is above the magic 120VI index number.
But the base oils are identified with the 64742-54-7 CAS number, which indicates a group II+ process where the base oil batch spends more days in the hydor-isomerization catalyst process to lift the VI from high teens to the 125 range.
In effect, these base oils are more comparable to a high quality Grp II+ and do not have the performance characteristics of full chemical synthetic fluids as found in some of the M1, Amsoil, & Redline formulations.
If we switch the focus over to the additive side, my pick would be the MC 5W-20, with the 150 parts of boron as a secondary anti-wear additive. The Walmart 5W-30 syn formulation has no significant amounts of moly, boron or magnesium and appears to rely on the higher than normal levels of calcium to provide secondary anti-wear.
My choice would be the MC 5W-20 option. And the member, who posted a picture in a recent thread in the Automotive General forum, of the odometer in his patrol car turning over 200k miles, is just another indication of MC 5W-20 being a proven performer in law enforcement, emergency & municiple vehicles.
