Multi weight dino
oil is made with the lower viscosity to begin with, for example 20W50 is 20weight with viscosity improvers to get 50 weight when at 100C.
Synthetic 20W50 starts at 50W and uses VI's to get to 20W at 40C. Assuming both
oil are run indefinetly eventually the dino 20W50 will be 20W once the VI are consumed and 20W50
synthetic will be 50W. I would rather have the 50Wt as opposed to the 20W once the VI are consumed.
VI do not have the lubricating properties of
oil and is why you want the smallest spread in a multi viscosity oil. Straight oil has no VI it's entire volume is oil. Synthetics do a superior job as compared to Multi weight dino's.
Most modern day oil are made for modern day cars looking at fuel efficiency and emmisions. They have extensive detergent packages etc. Brad Penn and I assume Joe Gibs don't care about emissions and fuel efficiency. There oil have 50% more
zinc and phosphorous which is known to harm catalytic converters. Kinda like an extreme pressure additive. That being said you could get a shelf brand oil and throw in some red line break in additive and get the same result.