For the viewport rendering, I wonder if you would get a speed-up by setting the view to either point cloud or wireframe. Or simply change the main viewport window to the outliner or something that doesn't require a preview, if you don't need to see it. From that standpoint, the time it takes to go through should be pretty much the time it takes for the dynamic solver to calculate. As for running it from the command line, that is more of a problem. I don't know of a way to do that either.