Good idea Garak! "Is it simply that there's no point in chasing one specification?"
Guess it may not matter below a certain %.
One criteria I can think of is in Wankel rotaries. I think they banned synthetics from use since they metered oil into the combustion chamber to lubricate the seals (generalization). So a low Noack volatility would resist the burn and maybe gum up the engine or something. I remember reading of some 'over-maintainer' that used syn despite online advice and the OM and had early engine failure.
FWIW, I have just kind of started to have a novice layman's understanding of oil analyses (my own judgement). And I am just trying to understand. Like, who here would want an oil with a 300 viscosity index and a 1.5% Noack?
The point of this thread, I think, is to question whether a lubricant that excels on paper and in tests will be 'good'.......as in, run smoother, more power, last years, not leak, handle cold starts, high temps, short trips, go the distance, lubricate the metals, keep them clean, resist rust, and other things we want out of an engine and oil combo.
Kind of like what do you want? More power, well okay your engine will only last a year before rebuild/overhaul. Want it to last forever without maintaining it properly? Well ok, it will have a lower power output, not be too smooth..
The cost, weight, performance circle comes to mind.
Sometimes I feel we get caught up in the statistics and bench racing. Wile my car beats your on corrected magazine tests, you beat me stop light to stoplight and lap me at the closed circuit.
Good day/night all!