The three following frames show that without AGEIA PhysX, the smoke is almost vanished. However, with Ageia PhysX enabled, smoke is present and more effects are offered:

Without Ageia PhysX

With Ageia PhysX

Without Ageia PhysX

With Ageia PhysX

Without Ageia PhysX

With Ageia PhysX

The scene with AGEIA PhysX enabled lasts at least 2-3 more frames, since smoke and wall fragments continue to fly around and fall from above...