I don´t get why would I have 6 buckets if I only have two possible processors calculating it?
The hyper threading tecnology let´s you use two operations at a time, so each processor can calculate two buckets at the time...2 processors 4 buckets. If you say u want 8 buckets and you only have 4 available, maybe (I´m not sure about it) it will give two to a single processor, so it will take two times more (so there´s no reason to do that). I don´t know how the processor will handle the extra buckets, but if there´s no possible resorce to calculate them, what I can be sure is that you will not gain from doing it.
I´m using distributed rendering on 8 HT machines, realy wonderful, having 16 buckets at a time in your image.
This is an interesting issue, I haven´t made a test to see what´s best, HT on or off.
Any coments on the subject?