The graphics fps are about 120/140, the physics per second are around 40, which seems to be the bottleneck, however cpu isn't maxed out, I've 4 cores out of 8 used at about 50/60% each.

What contributes to physics performance?

Are you running an 64 bits OS?

Yes

The CPU memory bus is in this case most likely the bottleneck.

The 64 bits version is faster for that reason. On slower systems however the physics can be the bottleneck.

Ok gotcha, thanks

Btw nvidia videocards support physics.
Xsp uses the videocard feature if exists or the physics are always made with cpu?

Because cloth collision with soft bodies is still beyond current hardware implementations we regrettably cannot use hardware physics solutions.

Also the multibody dynamics support in hardware is very limited.

Next version will have improved collision support to extent the use to systems with slower CPU and bus.