If you are worried about the lubrication in the valve train, I'd also study which oils have the best anti-wear package. Boron is a pretty effective AW additive per this article. The valve train (cam/followers) run primarily in boundary lubrication realm, so a good anti-friction/anti-wear package is important. The HTHS viscosity isn't a big factor in boundary lubrication, but perhaps it helps minimally by keeping the surface contact level slightly lower. Of course, the metallurgy of those components is very important, and if those are bad then no oil will cure or prevent those parts from wearing excessively.
"In addition to zinc, other anti wear agents such as Boron and PTFE are used in oils as sacrificial agents. Boron offers much greater protection than even Zinc by increasing the load carrying capacity of the oil by as much as 8 times in a 4 ball load test. It also showed a 12.5% decrease in scarring over a normal engine oil with a standard anti-wear additive pack and better than 50% less scarring than a base oil only 4 ball wear test. Apart from it's increased protection, boron does not increase emission levels and is safe for catalysts."
Anti-Wear Agents prevent wear from seizure or scuffing of metal surfaces that would otherwise rub or contact each other. They are normally zinc and phosphorus or other organo-metallic based compounds such as boron, and are sacrificial, decreasing throughout the oil drain interval. In addition to...
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