Tread wear has a lot more to do with how and where you ride, and may be affected by carrying a passenger. I have never seen any claim that tread life is different on a B-spec, but for any PR2 or PR3 tire the variation can be over 50% between riders...a range of 6000 to over 14000 miles on a set. With that kind of individual variation, mileage claims don't mean much.
My experience was the PR2 outlasted the PR3 by 30%. The initial traction and handling of the PR3 was a bit better especially in wet. Both tires suck at the end of life and will lose the last bit of tread really fast! You might see a tire that looks to have 1-2K miles left, and it could be gone in 500. This has led to many a tire-change away from home.