So, not being an expert on oil or engines I had to look up some info to understand the plain english of Markus's post.
HTHS
High Temperature, High Shear
https://www.motul.com/fr/en/community/373?
“Hot viscosity was measured until not very long ago only at 100°C, which is not very representative of the temperatures reached today by most recent engines. It was therefore decided to also measure viscosity at 150°C, and under a high shear rate, so as to really judge the capacity of the lubricant. That is what HTHS (High Temperature, High Shear) viscosity means.
The notion exists of High HTHS and Low HTHS: a Low HTHS oil has a lower viscosity at high temperature (<3.5 mPa.s) than that of a so-called High HTHS oil (>3.5 mPa.s). This notion is important as it allows the classification, on the one hand, of 'energy saving' oils having a low HTHS and, on the other hand, of high protection oils having a high HTHS.“
(I saw that Rotella T6 is 4.0, Mobil 1 0w-40 3.8)
High Temperature High Shear (HTHS) Bulletin | Driven Racing Oil
“Lower HTHS viscosity generally means a thinner oil which can improve fuel economy by reducing the amount of horsepower required to pump it throughout the engine. But a lower HTHS viscosity also usually comes at the expense of wear protection.“
Low SAPS
https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2868824
SAPS stands for Sulphated Ash, Phosphorous, Sulphur.
Low SAPS basically will show up as lower sulphated ash level on a spec sheet. 1.36 would be full SAPS. 1 would be mid/lower SAPS.
“Lower levels of SAPS are desired in order to protect modern day emissions systems. The way lower SAPS is achieved is typically by reducing the additive levels in the oil.”
“The higher SAPS oils are actually longer lasting due to the higher initial TBN (acid neutralizing ability) of the engine oil. “
From what I have found so far, Rotella T6 is low SAPS,
Mobil 1 0W-40 seems to have split this year to Full SAPS and Low SAPS
I'm still not clear on why avoiding this is important.
Mobil 1 product info sheet:
https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide-2016.pdf
Rotella T6 info:
http://rotella.shell.com/products/t6-full-synthetic/_jcr_content/par/textimage_1335213348.stream/1388525673850/2c4570ceb0dcc96c0e045d7d6f3c7796f77a84ed6a3d6752bb 50d245468c48b2/rotella-t6-brochure.pdf
We need more oil threads.