Hmm, 0W-20 vs. 5W-20. This discussion is similar to 5w30 vs. 10W-30.
One thing to look at here is the base-oil quality. Remember that, in the order of decreasing base-oil quality, PAO > GTL > Group III > Group II > Group I. We are not only looking at the viscosity performance here, which is probably similar for 0W-20 and 5W-20 at high temperatures, but also the base-oil performance, which at the least affects the oil-change interval (OCI), among many other things.
So, you're looking at 60 - 70% PAO in M1 EP 0W-20 vs. 40 - 50% GTL and no PAO in M1 EP 5W-20. To me it's no brainer that M1 EP 0W-20 far exceeds M1 EP 5W-20 in base-oil performance. In fact, M1 AFE 0W-20 also exceeds M1 EP 5W-20 in base-oil performance. If I had to pick one from these oils, I would go with M1 EP 0W-20 without hesitation, knowing that it has the best base oil. You care for a synthetic, right? Since synthetic is a loose definition, why not go with the best synthetic and have your money's worth. Otherwise, you can forget about synthetic and pick a conventional 5W-20 or 5w30 and save money.
In general I expect most 0W-20's to have the best base oils available out there. This is simply because you can't achieve the minimum-required NOACK along with the CCS @ -35 C performance required for a 0W-xx without using the best base stocks.
It's also interesting that 0W-16 has even better base oil than 0W-20. It's quite evident that manufacturers need to uniformly increase the base oil quality as the viscosity gets thinner. This is so that the oils can still meet the performance requirements as they get thinner. M1 0W-16 is virtually all PAO, which is unseen in API/ILSAC oils since the SM era.
Note: The remaining balance (percentage) is ester (probably 0 - 10%), Group III, viscosity-index improver (VII), and additives.
M1 0W-16: 70 - 80% PAO, 10 - 20% GTL
Mobil Super 0W-16: 70 - 80% GTL
M1 AFE 0W-20 SN: 30 - 40% PAO, 10 - 20% GTL, 30 - 40% Group III
M1 EP 0W-20 SN: 60 - 70% PAO
M1 AP 0W-20 SN: 60 - 70% PAO
TGMO 0W-20 SN: 80 - 90% Group III
M1 5W-20 SN: 40 - 50% GTL
M1 AFE 0W-30 SN: 10 - 20% PAO, 20 - 30% GTL, 30 - 40% Group III
M1 5w30 SN: 20 -30% PAO
M1 EP 5w30 SN: 20 - 30% PAO
M1 AP 5w30 SN: 5 - 10% PAO
(Compositions from
ExxonMobil MSDS)
