As far as bucket size goes, I have gone as low as 1 for complex scenes using the Global Illumination Python script for Poser 7. It seems to keep me from getting those error messages, which can get quite frusterating if it's been rendering a few hours then crashes on you.

But generally, I'll keep it at 32, 16, 8, and 4, depending on the scene.

                                                                                                                    

Poser 10

Octane Render

Wings 3D