wow 7% is still very good. I will maybe try that next time I change my oil.
I also read that the lower viscosity oils are more for colder climates .
It depends on what you mean by lower viscosity. M1 0w30 is actually thicker by a small amount at operating temp that M1 5w30. It is, however, thinner at startup and temps below 40C. So, it gets to the engine lubricated parts faster, runs thinner while warming up, and then is slightly thicker during steady-state operation. What's not to like?
The better fuel economy (7% seems high) probably comes from the driving profile, if you are doing short trips that never get the engine up to temp, then the oil that is thinner at lower temperatures will give you less pumping losses. If you were doing long highway trips, there should be no difference between the 0w30 and 5w30 mileage.
Personally, I use the M1 0w40. While it is slightly thicker at temp, it has the advantage of being thinner on startup. Also the 0w40 will shear down slightly as it ages, to counter oxidative thickening as the oil gets older. Currently running 10k OCI.
As far as RP goes, while it isn't crap, it also doesn't seem to do any better (or in many cases as good) than M1, PP or RotellaT. Why pay more for the same or even less performance? If you want a oil at that price point that actually does perform better, go with RLI BioSyn, arguably the best oil currently available. I don't, however, feel that it is worth the price premium either. If you are running a DI engine (FX50), then it is a whole 'nuther ballgame.