I love OIL threads, so entertaining.

So, if you go by the rules in USA, Shell Rotella T5 is Synthetic. But in the Euro rules it is just a highly refined dino oil... But it is still a good oil.

Zinc and Phorphous should be above 800 PPM for a slider cam. But this level will kill a CatCon so that is why most modern oils do not have any.

Most oil fanatics will NEVER blend different weights or brands. But if you do blend, kind of know what your mixing. For a street daily driver, mixing can be OK if your sphincter muscle is not too tight.

I have a 110 volt hot plate that will keep food at 145 to 170 degrees F. I do this outside in the driveway, not inside the garage... I would pour three quarts of my base stock oil into a 4 quart Revele Ware pan. Then I'd add the GM EOS Zinc additive, 1 can of STP and heat it up. I mix it real well and then pour some into the oil filter and the rest in the engine and top off with base stock oil.