I've run (4) Bt-021 rears, as well as RoadSmarts and PR2s in the past. I tend to ride hard, averaging 4k per rear tire.
RoadSmart: Stickier, better wet-traction, worse life (3 - 3.5k)
Bt-021: Less grip, especially when cold, worse wet traction, better life (4.5k usually)
PR2: Far worse...