OK, so the 5W30 is a semi-synthetic, and the 10W30 is a conventional (mineral) oil. Both are API SP.
This matches what blenders here have told me. A 5W30 needs thinner base stock to meet 5Wx, and some of this would need to be synthetic (Group-III) to meet other SP requirements like the Noack volatility limits. However a 10W30 can be made with thicker base stock to meet 10Wx, and it would naturally have lower Noack, so it can be all Group-II.
This shows how good the modern API SP standard is, and any oil that carries it is a good oil.
It also shows that being synthetic is more important for thinner and 0Wx oils, and why old school 15W40 HDEOs performed so well in their heavy duty applications.
In Australia we get Castrol GTX 15W40 for cars that has both American API SP and Euro ACEA A3/B4 specs, it's a mineral and it's as cheap as chips. You can bet any car sold in Australia has a significant amount of owners running a dual rated mineral 15W40 in it. Given our hot climate we can run this year round. Given that our traditional birth right oil is 20W50, this 15W40 is also our modern thin economy oil.
I was at a fuel station recently, and a guy in a nice business suit with a new shiny Audi pulled up. I assume he had a low oil light showing. He just ran to the store, grabbed a 1L (~quart) of conventional 15W40, poured it in and drove on. I'm sure of two things, no - it didn't carry the correct VW specs, yes - his car will be completely fine.