I'd like to second this thread...
I'm brand new to MeshMixer. Looks like what I needed until I finished some tutorials and loaded my first model. It was way-outside the design parameters of the product. The model has 5.7M triangles. I let it run for 24 hours doing Overhangs with default settings. I can confirm that it is doing only 12-13% CPU on an i7 (4 cpu / 8 thread) running at 3.5GHz. Extrapolating the progress out predicts a 51 day processing time. I killed it! 🙂
It has been my experience writing C#/C++ math intensive, n-squared, n-cubed type 3D matrix applications that I can get approximately 5x performance gain on my i7 when using eight threads set as background and with lower than normal priority. The UI will still have usable performance for things like email and light editing.
With the advent of some of these killer CPU's coming out from AMD with 32 and 64 cores, I would think this 51 days would easily be chiseled down to ~1 day. I was thinking it was about time to upgrade my antiquated i7. However, I don't think it would make much difference if I had 64 cores over my lowly i7... at least with MeshMixer.
P.S. - This was just a test. In a practical sense, I do plan to cut it up into multiple pieces and reduce the resolution on the model. MeshMixer still looks to be the best tool for the job. Multi-threading would just enhance the product greatly!!!!