It also hit me this evening that while I feel like this simulation isn't running all that fast, the reality is that it is running in close to real time. It finishes an orbit in about 7 hours. The real material in the F ring takes almost that long to get around Saturn. So on the whole I'd say that is pretty good. Maybe after this one has gone far enough to wipe out the transients I can consider scaling it up a bit more. I'd be really interested in seeing what happens if I make it so that Prometheus really does run into the apron of material at the edge of the ring. I expect the computers will be less than happy about such an experiment though.
As a side note, on the recommendation of Matt Tiscareno I did some simulations on moonlet stability that didn't include the background. Unlike previous work by Porco, et al., I am not putting a large central core into these moonlets. I am assuming all particles of nearly the same size. This is significant because the Hill sphere of the large body can enclose nearby smaller bodies when two bodies of the same size sit largely outside of one another's Hill spheres. I was able to find a configuration where a moonlet was stable without background material and got broken up when background material was present. The moonlet was made as a lattice roughly filling a triaxial ellipsoid at 130,000 km from Saturn. The lowest density I could get to be stable i this configuration with a 2:1:1 ratio was a bulk density of 0.7 g/cm^3 or 1.0 g/cm^3 for the constituent bodies. Even with that high a density, it got knocked apart when I put it in a background. I'm not going to be doing too much more work on this right now because Crosby found it interesting and will likely work on it as part of his senior research project in Physics.