I run what the car calls for. 04+ 3800s call for 5w-30. 3800s before that called for 10w-30.
And RP is like $7 a quart here.
It does work. Documented proof is out there from independent tests. Plus my improved gas mileage as well as longer warmup times point to reduced heat and friction. I'm sure you saw the pics of how clean it was inside my engine. RP does a great job keeping it clean. Pop open cars that have used crappy oils and look at the mess you find.