Since retirement, I work part time in a automotive shop that services vehicles for large fleet operations such as Fed Ex. I can tell you that, for most people, Mobil 1--which I use in my Solo cars--is generally a waste of money. The key to engine life lies in good scheduled maintenance. Don't get me wrong, Mobil 1 is the only
oil I would use in situations where load demands are high such as in towing and hauling where high temperatures are sustained for long periods of time. But, for the most part, the average guy just isn't presented with that problem.
We have a early 80s Nissan pick up that has had its
oil changed like clockwork every 3,000 miles. The engine has 755,000 miles on it. We have gone through three transmissions over the life of that truck, but the motor has never been disassembled. The same situation hold true for a "tin can" Chev Corsica that has had the same treatment. 567,000 miles and it runs fine with the exception of a noisy internal cam tensioner which is an inherent flaw from the Factory. Both of these units use fossil 5W-30 Mobil.
Many of the manufacturers such as Ford, Honda, Toyota & Subaru have been moving toward 5W-20 instead of 5W-30 as a requirement. We have a lot of diesels (Benz; 7.3/6.0 Fords) that have over 350,000 that use Mobil DelVac 15-40. No problems there, either.