Some HDEOs have forgone gasoline specifications. If it's in what's known as an ILSAC grade, that is, 0w-30, 5w-30, 10w-30, even if they have a CK-4 listed first, they do not get a phosphorus waiver for SN. So, they must have 800 ppm or lower. For Delvac 1 LE 5w-30, which is still CJ-4/SN rather than CK-4/SN, it would never be an issue, because its E6 specification (same as Shell Rotella T6 Multi-Vehicle 5w-30 in CK-4/SN, Delo LE 5w-30, and a Castrol variant) already limits the phosphorus to 800 ppm, irrespective of it being CJ-4 or CK-4. Each company can handle things differently based upon their own plans. Delvac 1 LE 5w-30 is CJ-4/SN as before. Rotella T6 5w-30 is CK-4/SN. The Castrol version is diesel rated only, despite being E6 and meeting any SN phosphorus limits. Now, with more ordinary CK-4 lubricants, like the 10w-30 HDEOs we'd see, when going CK-4, they either don't get to have SN, or they cut phosphorus. With the 40 grades, they formulate and label in what way works best for the oil company's product strategy.
If wanting to talk dexos1, there are a couple things to remember. Let's look at the original dexos1 specification. It wasn't terribly demanding, and could be met by a blend. The Vette synthetic spec seemed to be more rigorous. The main thing was to have a reasonable oil above and beyond ILSAC for reasonable OCIs. Most synthetic 5w-30 ILSAC options on the market at the time, particularly the majors, exceeded it already. Things are a little tougher these days with LSPI and reduction in calcium. Incidentally, most synthetic HDEOs had already done that long before dexos1 Generation 2 came about. Less calcium and more magnesium is an effective way to keep both the TBN up and SA down as required in E7, E9 lubricants. That came about generally with the CJ-4 rollout.
I'd have little doubt that Rotella T6 Multi-Vehicle 5w-30 (or any other E6 lubricant) would be suitable for use in a GM engine calling for dexos1 5w-30 of either generation. An E6 lubricant won't meet dexos1, technically, though, either Gen 1 or 2, because the HTHS is too high. It's simply thicker than what GM has been seeking for most gasoline engines for a number of years. Aside from that, most E6 lubricants would easily go to the OLM limits of a GM vehicle, and much longer. An E6 also won't meet dexos2, incidentally, because, while HTHS is correct, SA is too high.
I wouldn't say that Rotella T6 Multi-Vehicle is the most popular HDEO. I would say that an E6 lubricant like that "should" be the most popular synthetic HDEO, given the builder approvals and versatility, but these things take time. Trying to usurp 10w-30 or 15w-40 conventional HDEOs will take a lot of work and luck. I've noticed that here in Canada, the E6 lubricants I've looked at have been attractively priced. Availability at ordinary retail outlets isn't where it should be, but for anyone buying from a commercial outlet, it's very easy and cost effective.
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