Here are all about the num of entities in each scene and some information:

Tower scene:
FPS: ~20
Physic Objects: 235
Number of physic contacs a frame (max.): 1669

Walls scene:
FPS: ~15
Physic Objects: 366
Number of physic contacs a frame (max.): 2452

Super tall tower scene:
FPS: ~20
Physic Objects: 265 (looks more than 265?!)
Number of physic contacs a frame (max.): 1349

Stability: Because I use many physic objects at the same time, I sometimes had a problem that some objects didn't move.
Btw: I've tested all the scenes in A6, too. I hadn't notice any differences.

@MrCode: Nice idea, but I don't think this would work because it's already using to much performance.

@Pappenheimer: Freeze_mode=1, das friert doch alle Entity-Funktionen ein

Regards
TSGames