I've always based my opinions on oils from engines I've stripped and been able to find out what
oil was normally run in them. Wear is kinda tough to gauge as the engine design itself has a lot to do with it. One of the worst was the Pontiac BB's (terrible oiling system). The best I've seen being Oldsmobile. (great oiling system + high nickel castings) The Pontiac engine seems to wipe the bores out no matter what
oil was used, the Olds was just the opposite.
Valvoline for some reason keeps things pretty clean with little (if any) build-up on the cylinder heads. Quaker state leaves so much wax in the heads you half expect to see a wick sticking out of it. I've only pulled apart a couple engines that have run synthetics, both were extremely clean. Kinda wierd not to even see any varnish with this stuff.
What little I've heard about RP over the years has always been positive, but very few people run it because of the high price.