Torco...NEO...RedLine...Royal Purple
From what research I've done, Torco and NEO are as close to a 'true' synthetic as you can use. Both use ester and di-ester base stocks. Mobil 1 and I'm SURE that Amsoil use PAO's as a base stock. There was an episode on TNN ( Horsepower TV ) where they switched out the dino oil with Royal purple and it showed a significant HP increase. Does RP work better than M1...maybe...is M1 a good oil...yes.
All I know about Amsoil, is that, I just won't buy into the extended oil drain idea, even with a quadruple heart by-pass, triple filter with an over the top coffee filter and cotton gauze tea strainer.....SORRY !!!!
Right now I switched to M1 and an M1 filter, ran it for 3300 miles changed the filter to a Motorcraft FL-820s and I will leave the same oil in there for another 2700-3000 miles. At that point I will take an oil sample and send it to BlackStone labs. I used to get 6K miles from Mobil's Delvac 15w-40 diesel oil ('97 F250HD Powerstroke ) and if my lab results from the diesel showed that I could get OVER 6K miles from the same oil/filter combo, I should get about the same from M1 by changing the filter and topping off the oil.
I wll post the results ASAP.
BTW, I do about an 80/20 hiway to city driving style.
JR