I use it in my '89 GTA. The shortblock has 173,000 miles on it, and the car still gets raced occasionally. Oil pressure has dropped about 10 lbs over the last several years from bearing wear, so I use the M1 10W50 to keep the oil pressure up so I don't spin a bearing. The car is a fair weather toy.
A while back I bought a bunch of it on sale at Target, the EP version, for $1.09 a quart. At that price, I figured I'd MAKE it work, so I mix it down with M1 5W20 for our 97 Avalon (plus LC). 90% city driving, 4K OCI's. Oil looks like honey on the dipstick at 4K.
I am thinking of switching over to it for my 393w.
I am currently using Shell Rotella T 15w40, but hot running pressure is only 45psi, I think I need to step up to xw50 to get the pressure to atleast 50psi hot running?????
AN interesting point. I'm beginning to wonder if it really matters all that much in most applications. I've used 10W-30/15W-40/20W-50 in dead winter, and 5W-30 in early summer, with little discernible difference.