caustics III've optimized the scene to a satisfying degree.
This took 27 minutes and 30 seconds to render, 318% faster. Almost as faster as blender internal, and much better looking. Unfortunately, it's still too slow for a full 1080p render.
In related news:
Water simulation with caustics. from Samuel Bierwagen on Vimeo.
Fitting with the "whoops" nature of its start, the finished product came out at 100 fps, rather than 25, so it's four times faster than it should be. And, of course, the vimeo codec obilterated all the fine detail. Oh well.