I would add my agreement to the OP's finding on the 0-40 RL. I alternated between various weights of Motul, M1 and RL over a three year period. Some readers may recall I was having oil consumption problems with the aluminum LM4 5.3 in the '04 Rainier that came to us when my MIL passed. 800 miles to the quart. Stuck rings and a poorly designed EGR system seemed to be the causes in the end. Two passes with the RL and a change to an updated valve cover (embedded EGR system) and oil consumption has finally gone to 6,000 miles per quart. I am guessing that the high detergency of the RL did most of the work. But back to the 0-40 weight specifically. This motor also has the dreaded piston slap when cold. The 0-40 RL was the only one that solved that (admittedly likely more mental than actual) problem after going through all of the other weights (5-30, 5-40, 0-40's of the others, etc.). When the Motul Xcess 5-40 that I re-ran to check (it's a lot cheaper) runs its course the RL is going back in, hideous expense and all. And yes it even sounds smoother.
Anecdotal but there it is.