The A is supposed to be for colder temperatures, from what I've heard it holds up better than the old PR3 as long as it's cool out. As for the B, I was getting 6+ sprints out of them last year on a 600 at a mid-pack expert pace, and they were still sticking pretty good for a practice day afterwards. Not sure where you're getting the 2 sprints thing, I'm sure a 1000 will cut down on the lifespan but it shouldn't be that much.
