I now have 16,634 miles on my PR3s. I mounted them with two ounces of ceramic grinding media ("ZIRMIL" 2.3 mm) in the front and three ounces in the rear for balancing, and have no visible cuping on either front or rear. The tires both still look good, in fact, with little or no evidence of "squaring off."
I measured the tread depth when new as 0.159" front, and 0.237" rear. These depths are now 0.065" front and 0.084 rear, for 0.094" of wear on the front, and 0.153" of wear on the rear. Assuming the same rate of wear, I should be able to get another 11,502 miles on the front before the tread grove at the center just disappears, and 9,132 miles on the rear. It's tempting to try it! The groves are deeper away from the center, so I guess I ride conservatively.
Almost all of these miles were at about 50 mph or less, with only a few hundred at freeway speeds, and on fairly new tarmac pavement. This bike is my daily commute transportation, and there were only a few "ice" days this year here in Florida.
Needless to say, I'm delighted with this result. PR4s next time! About next fall, I think . . .
Bill