Actually, in this case, 3D dof would help a bit as there are foreground elements overlapping background elements. And with 5DHD sampler it really should not take that long :) I am curious if you could try to enable DoF here without changing any other settings, let it render for same time, and check if it comes out with worse quality ;)
Forestpack guy mailed me a few days back asking me if my autumn forest render is done in forestpack. I had to say no, but i think they are desperate for pictures, so you could send it to them, and it could be a good promo for both you and corona.
Picture itself is really amazing.
Oh, and disabling sun in reflections and refractions now works correctly, so you can disable sundisc reflections to get rid of those hard bright hotspots if you ever encounter them. This scene might not be the case, but overall, in natural scenes, they like to appear a lot ;)