We just finished upgrading X-Morph: Defense from PhysX 3.3 to PhysX 3.4. It gave us a massive performance boost, with rigid body collisions 2-3 times faster then before (primarily convex vs convex)! The performance gain is only from using CPU simulation. The port itself was relatively painless with NVIDIA quickly patching up one of the bugs that we found with join break force calculations.
We are planning to check out GPU physics simulation in the near future to see how far we can go with pushing the amount of physically simulated debris (we were told that we should be able to have thousands of objects without a noticeable performance hit). In the mean time check out this short video showing our destruction system.
https://youtu.be/7t5sqbZIi8E