I am an Amsoil dealer and their oil is very good quality in a 6-month or 7,500 mile formula (XL). The just released a new product called OE to mach the car manufacturers drain recommendations.
This is my opinion: Clean your engine with flush to remove all the gunk from years of burnt oil deposits. I run a pint of Marvels oil in my car for at least 1,000 miles before I drain the oil and it cleans the piston rings and dissolves some of the deposits left by the oil.
After 800 miles, the 5w20 oil starts to shear back into a lower film strength, this is typical of any multi-grade oil and causes undue wear (Honda's are bad for noisy pistons from that). I see no harm in running 5w30 engine oil or an additive such as Lucas or STP to add to the oil cushion between parts, it also adds to the anti-wear properties of regular oil. When I run regular oil, I add 1/2 bottle of STP to help the oil to cling to the bearings during start-up.