Nice render!
I usually end up using plop render to final render smaller parts of the image at a time so my machine only has to make the calculations for that part of the image instead of the machine taking the whole image into its calculations and eases some of the frustration of having my computer tied up for such lengthy time periods That way you can save its progress more often and it comes back in at the same point of final render every time.

I love Bryce but its one major shortcoming is the render engine. I really don't see why Bryce has such great potential built in but is held back because its rendering engine isn't optimized to handle the task efficiently. What's the point?
If there is going to be a V7 of Bryce, I hope the rendering engine is THE most improved part of the new version. I would also like to have an irregular plop render capability instead of just a variation of a square version...that would save a lot of useless rendering of non-essential parts of the image everytime just to get the part rendered that you want rendered!