This should be a separate thread, but it's related: I discovered a trick long ago on how to drive kinematics with ICE and have it be quite fast, easily pushing >1000 nulls in real time. You build a single polygon mesh with a separate square for each particle, driving each square from the particle's SRTs with a simple ICE op. Then you create a cluster on each square and constrain scene objects to the clusters.
I had a script that set the whole thing up, so you could select a group of scene objects, then pick a particle cloud, and it would constrain the scene objects in the order you selected them. This was a necessary workaround back in the old days when Arnold wasn't working with instances, but the tool came in handy for all kinds of situations to drive scene object kinematics based on particle sims. When they gave us ICE kinematics later on, the cluster constraint trick still performed much faster and was more stable so I kept using it. This same technique, BTW, allows you to use deformations to control SRT movement of scene objects. Once your objects are constrained to geometry, you can apply envelopes, lattices, or whatever other creative setups to animate their motion.
