re campag ball quality. I don't know what the current state of affairs is but the legend on every box that Nuovo Record hubs came in used to say 'con tolerenzia di un millesimo' which roughly translates to 'with tolerances of one micron'. This could be hyperbole, but if not it suggests that the balls inside are Grade 5 or better.
I let some water get into some NR pedals and I tried to replace the balls because the old ones had started to look dull; the pedals didn't run smoothly again until I put the old balls back. Investigation showed that with cheaper balls, only three were touching both raceways at once.
Re using cheap balls in cheap, knackered headsets; when the raceways are lumpy to the tune of 100 microns or more, ball quality is almost irrelevant. If it were a hub or something it'd be scrap, or due an inspection after another thousand miles, tops. But with the right grease (loaded with solid lubricants + EP additives) and a careful setup, a headset will work OK.
The reason the grease needs solid lubricants and EP additives is that in a bearing with lumpy raceways, you want the balls to slide easily if they need to. This is (at low speeds/repetitions) preferable to a pure rolling contact if the balls can't roll in the correct way, e.g. because the surfaces are so lumpy. Sliding and scuffing (as permitted by solid lubricant additives etc) are however fatal to high-speed bearings, which is why you won't find bearing greases with high quantities of these additives; a grease that is meant for something like an exposed gear train (including low speed bearings) is a better idea.
Whether bearings like hubs etc are more like low speed gear trains than high speed bearings I don't know; but I do know that nothing I have put the gear train/low speed exposed bearing grease in has unexpectedly worn out or broken yet, and it has been a long time....
There is arguably little point in spending a fiver on balls for a cheap headset; a new headset will cost about £10 or so (but may take hours of wasted time to correctly identify and source these days....
)
A Brucey top-tip; if you are converting a new/unworn headset of reasonable quality (eg a Tange one) from clipped balls to loose balls and you only have cheap balls to hand, you can do yourself a favour by
a) carefully extracting the balls from both clips
b) use those balls in the lower race
c) use the cheap balls in the upper race
The resultant headset is usually better than it would be with cheap balls throughout, and probably as durable as if it had posh balls throughout; the lower race is the one that benefits most from better balls.
cheers
