Welcome to the club Flip. I took the plunge, @10/qt just before Smashville.
I can't remark on the linear aspect. Does that mean it shifts easier? I find that is the case and going into 1st is considerably smoother (I never did have to muscle it into 1st). Would this have been the case with Mobil 4T, I'll never know.
Mine too became quieter, so much so that I discovered a new rattle, at about 1900-2100 RPM, above and below that it's not there. I think it's radiator screen, and chrome surrounds. I'm guessing the engine vibration at 2k is just right to get that rattle going, then it's gone. Rusty says he stuck or hung some Trojans here and there to rid his beast of that rattle.
My mileage went from 33 to 35, and nearly 37 with all interestate miles. With my recent add-on (TB) I know that's going down the toilet (too much fun with the new found power).
The most I've gotten was 39 on my first ride home from the dealer, in chilly December.
I too use the used Mobil in various lawn and garden equipment.