The closer the two numbers are in the multi viscosity rating, the better. Basically a 10-30 lubricates better than a 5-30 or 0-30. There is no point in running the wide viscosity range oils unless you live some where cold enough to require it.

 

We had and have both our trucks on 10w-30 mobile1 after they hit 12,000 miles. Our 91 350 chevy had 255,000 miles on it when we sold it and it is still running today. That engine never had valve covers off, oil pump changed, or timing chain. Our current 99 5.3 has same oil in it and currently has 180,000 miles on it and a lot of that is hard miles. This motor and truck for that matter hasn't had any work done to except brakes & fuel pump. We constantly overload the truck with weight totally over 7,000#. I should also mention our oil changes occur every 10-14,000 miles. Great product.