It depends what you mean by a hike in the forest ! I have taken my 500mm , mounted on a tripod and carried over my shoulder, for several walks of a few miles. I would avoid doings so if possible as it's a fairly heavy combination. The 400mm and 600mm would be even heavier.
I wouldn't take my 500mm without the tripod either. If you hang it on your shoulder by the lens strap, the lens hood would be somewhere around your knee. I couldn't walk around like that, too uncomfortable by far
If digiscoping was as good as using a body and lens I don't think there would be a market for the latter.
I would think VR is more useful on the 500mm as it is just about hand holdable, in my opinion the 600mm isn't.
As for which one you would choose, it's always a compromise.I am glad I chose the 500 as I can take it as hand luggage on a plane, it weighs less to carry and I can use it without a tripod for BIF at a push ( but not for long !).
I will always wonder if I made the right decision though as you often look for that extra reach.
Which one should you buy ? I would get a 300mm f2.8VR and a 1.4 and 2.0TC111 as that covers many more options especially portability and should be cheaper too.