[SIZE=10pt]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. [/SIZE]
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 grip, Far better life (6k), Just not worth it, for me. It's really a Touring tire, not a Sport-Touring tire.
Metz Z6: Handles like a drunken pig. Long-ish life. Also not worth it, to me.
Shinko 005: I should've known better. Don't bother.
FWIW, I'm very impressed by my first ContiMotion. If lifespan is adequet, I may not switch again.