River sim I did a few months back for fun. I don't remember all the specs exactly (I've since removed the cache files). The sim ran overnight, and was about 30 million particles. The renders were pretty quick too (mantra). It's using a custom vorticity setup I've been using for a while (tracks with the fluid and fades out over time) for the 'foamy' areas. I did take the render one step farther with the shader (added volume under the surface and better driven by my vorticity attributes), but hadn't gotten around to getting a full sequence rendered. I'll probably re-sim / re-render soon enough.