matriax, here are capx's to compare the tower building performance of Box2D+, Physics and Chipmunk.
On my laptop I found they could all build tower heights of 30 rows without any problems in behavior or performance. Higher than that and cpu increased to max / the fps reduced and each plugin then misbehaved in different ways. Chipmunk towers would fall down to the right whereas Box2D+ and Physics towers would slowly deform before falling down. To be honest, I think that Physics had ever-so slightly the best performance, then Box2D+, then Chipmunk.