Cranky-
I'm no expert, but with forty years experience diagnosing, repairing/replacing bearings on pumps, motors, fans, etc, I've learned a few things.
I agree with your feelings about the probable damage from the difference in bearing grades, but I feel it is likely a very small amount. 99% of bearing failures are from one or both of two things: Heat and contamination. I don't think heat (except from sloppy torch work) enters the picture for bikes. Either grade of bearing ball will be damaged or cause damage when any dirt or grit- even dust- enters the picture.
Which is why I toss old bearings. They may be perfect, but I don't think I can keep the entire job 100% clean on reassembly.
As soon as the 2017 Beater Bike Challenge is over later this month I'm going to experiment and try what I've been reading about on BF lately and convert my Zephyr zombie to a sealed cartridge setup.