I ran Valvoline ML SB 5W-30 for 30k miles in my vehicle which has a GM aluminum 5.3L V8 with no AFM. It consumed the Maxlife at a rate of about 1 quart per 1,500 miles or so. I have no blue smoke and no apparent leaks or drops. Coolant does not show signs of contamination.
At ~85k miles, Nov2013, I switched to M1 0W-40. I've read that thicker oils may help curb oil consumption. This vehicle is also a short tripper, so I'm concerned about fuel dilution.
Oil consumption has not changed (yet). Fuel economy has not changed in any meaningful way or at least not in any way I can attribute to the oil. A 5,000 pound SUV with a V8 is a gas pig.
I have not noticed any changes in cold cranking, even at -6*F.
After looking at various posts on this site, in the PCMO section and UOA section, I have yet to see any proof that M1 0W-40 (or any other PCMO 0W-40 or 5W-40) caused problems for an engine. If these engines are operating in bypass for a significant amount of time while running xW-40, it does not seem to be hurting them in any appreciable way.
Dumping M1 0W-40 into my engine did not result in anything amazing or magical. From the driver's seat, it appears to be performing as well as the ML SB 5W-30 I had in there prior. I have enough left for at least 1 more oil change with it. After that I plan on trying QSUD 5W-30 or ML SB 10W-40. Why? I have them on the shelf.