I’m still trying to figure out what differences exist between these two specs. They seem to have a lot of the same types of tests. The one that stands out is that for C6, it is advertised as a “stay in grade” oil, meaning that some measure is in place to prevent shear. I’m assuming SP has something like this too, but I really don’t know. The only two highly available API SP oils that also carry C6 are Mobil 1 ESP 0w20 and Castrol Edge EP 0w20. Both start out pretty thin, but I assume that neither shear very much. I don’t think either use a lot of VIIs either.