I'm not neccessarily in the thicker is better mindset, because it may counter the lubrication of upper cylinder rings as hinted in a report by Shell I believe,....
HTHS benefit are there with these oils, but arn't everything. I'd figure these oil weights would better serve low rpm/high load situations rather than high rpm/high load situations. Just a thought.
They say that synthetics can often be formulated without VII unlike the standard petroleum lubricant of like grades. Perhaps this spread for a synthetic contains like quantities of a closer spread, more commonly used viscosity in a petroleum base lubricant? Anyone have the concentration numbers of VII for comparisons sake? One then will suffer from shear related viscosity thinning unless they are shear stable.
Would a shear stable VII not sludge as mentioned if this is caused by it's shearing breakdown, or is this thermally related - thermal decomposition/depolymerization?
One last question...when one is to consider the engine fully warmed-up and theoretically the wear rate has thus stabilized within designed constraints, the oil has reached a viscosity value for which design considerations have been made. Using a higher weight oil, unless leveled warm-up temperature rises to then again reach the designed oil viscosity value, it just might not reach the otherwise warm-up condition as far as wear, etc. If such the case, then viscosity maintenance for the sake of all out equipment protection no matter the ambient condition, would best be served via thermostatically controlled, full flow oil cooling. The engine coolant system helps to a degree, but when it comes to extreme conditions, it's only so effective at wicking the heat from the block (in direct thermal transfer).
Sorry for the side-step.