End of the threads
Just to follow up the previous post: The render has now finished, after about 2 1/2 days, and 530 hours of CPU time. The experiment has to be declared a success, since this would easily have taken 400 times as long to render on a single thread without the filled-square bypass algorithm. That's 2 1/4 years. Puts things in some perspective, I'd say.
The full image is here