FBinNY 

I bought my first Campagnolo Record equipped bike in 1967 and, like you, enjoyed many 10s of thousands of trouble and wear free miles.

But, I chalk it up to better steel and greater precision in cups and cones rather than better balls.

The difference in the tolerance if G10 vs. G25 is miniscule compared to the precision of the other parts, and certainly far smaller than what anyone could sense in a manual bearing adjustment, especially those assembling components in production.

In any case, your analogy is flawed. Big balls don't get squeezed into a tight space. Instead the axle is triangulated between the three closest balls, with the other balls doing less work, If 3 large balls are roughly equally spaced, all is good, but the odds are that they're not, causing the axle to and down as smaller balls pass below. It's not much and bearing can handle it, but harmonics can make that tiny movement problematic at high speeds.

So, I'll trust the judgement of folks at bearing companies like skf who reserve higher grades for especially demanding applications.