Think you'll find that the V.I. (viscosity index) is a Biggie in all oil specs -- and as easily tailored/measured for the syns as the dino. Granted that the curves will still vary a tad VS standard measuring points. (I use 5-30, for ex. == mfg. recommendation for temperate region.)

Apropos, when I first got my new (old) wheels, I compared a huge chart of specs - from Amsoil (clear spec-winner on most counts, but V. expensive - and I'd have had to have it shipped = more $, hassle) -- on through Mobil1, several other syns and many dinosaur blends.

It's not always a "doesn't matter which type/blend/brand", if you pay engineering attention: I went with Mobil1 -- not for any hype about 'syn' VS Not, nor emotional attachment to The Best-whatever. No sirree Bob - M1 had the lowest ash residue of all, save Amsoil.. but close enough.

Why care about 'ash'?

Well, all engines have hot-spots of a sort, often where oil galleries / water ducts have to make sharp turns or where surfaces are too-far from the cooling water-or-oil, because of shape constraints. This level of instrumentation data from the prototype NEVER gets revealed to the proles, for all sorts of Capitalism obviosity..

But what you know is: if you blast up hills in the torrid zone, you Will be carbonizing more of that %tiny part of the sump-full than usual. These coffee grounds / carbon globs are supposed to be taken out by the filter
[too long.. to go on about why that sometimes gets bypassed or.. stuff drops direct to oil intake screen, before the filter stage.]

Turns out that I had some data from Actual long-term Use re my particular model.
In brief, the fine-filter screen over oil pump inlet -- is a tad Too-fine. And while many of these engines have exceeded 250K miles-not-km with no sweat -- several abused ones have demonstrated the dread clogged screen: the remedy for which is expensive for the fastidious, or drastic (poke a hole in screen via a hole in sump = a sane solution for an old engine in an inline FWD config. But Ugly.)

Ergo: sometimes ash Matters - but usually, one doesn't have the data to know whether One's Magnificent model is much of a candidate for the above scenario. Still, the more expensive your engine and its labour rates, the more appealing the 'cheap insurance' value of such nit-pickery. I wotted. Besides, it's fun to run the numbers.. but just - now and then. Right?