, and sample every direction as evenly as possible. This only required slight modification to my path tracer, and does not introduce any bias. There are numerous other subtleties, but I'd rather not go over all of them, because if It is a unique idea/implementation, I could write a paper on it, which would be nice.
With the modified balance heuristic at 51 spp at about 20 miniutes:
without the modification at 81 spp at about 30 miniutes: