Wow another local. Right down the road!
In a nutshell:
The Series 2K's have a higher ester base. While in theory and on the lab bench, esters are a more robust group of organic chemicals, than say PAO or the mixed aliphatic hydrocarbons that fall in Group I, II and even III, The S2K 0W-30 in real motor oil use suffers from some of the same issues as Redline (overpriced for the miles/time used). Advertised to go 35K miles OR 1 year. Not many folks go 35K in one year. The oil can go 35K highway miles IF conditions are perfect.
The S2K also has greases, etc. The best product in this Series is the S2K 20W-50. This is a killer oil, worth the money, and is not recommended for 35K
S3K, ditto but a more robust TBN, etc diesel oil.
XL is indeed a robust group III oil. It is not simply a relabel. It is recommended for 7.5K max OCI's. But yes it is API certified.
Remember extended OCI's are very particular to the oil, the car, the driving habits, etc. Oil analysis is a powerful tool and I do not recommend extended OCI's without analysis.