I think some guys starting last year or two have felt the same way, that even finding the correct redline for any engine can be a process, but it is the brand keeping most hemi's the quietest. 5w30 for hemi 6.4 seams a good choice, 0w30 is more popular then ever 5.7 in cold places benefiting guys even at 30-40f. Find something that sticks and ride it till it don't. For guys in warm places start thick and move down if needed, 5w30 for me thick for 5.7. For people in the cold, start thin and move thick, 0w30 likely is the choice.