I'm very sure we can shave hours off the time it's predicting.
This render that I set up last night is a modification of an earlier render if mine. I added water and other stuff to it had all the same element as your render does (water, lots of trees, stones, IBL lighting etc).
This one took 2 hours and 12 minutes. It's still a bit grainy but you'll agree that less than three hours is a significantly shorter render time than you were getting.
Before you start it going again, could you post a screen shot of your render settings?
It was the IBL and the fact that I had 16 rays per pixel though I was sure I dropped that to 4. My bad.
I've changed the render settings, turned off IBL and did a render in 12 minutes. It's too dark, but I don't care, I now have a better base to work from, and I'll probably skip IBL altogether unless I do a new 'final' render overnight.
I'm still very very angry. I've changed a tree because I didn't like the way the leaves were rendering up close, and now I don't like this one either. The trees in Bryce are pants up close. Chohole told me that herself a while ago but I do like to find out these things for myself!
The water looked better WITHOUT the IBL, which was surprising. I think I'll still need another light source if I don't use IBL though.