Good point, Bob. I think because I shoot really wild and easily spooked critters, most of the time in tight quarters of heavy woods, I best stay moble and shoot hand-held. I can do that with my 200mm f/2.8 (with the internal IS on) about as well as I used to do for regular shots with a 50mm. Pentax offers a pretty good 300mm f/4, but I don't think I could shoot that hand-held except in the brightest light. If they made a 300mm f/2.8, I might consider it.
I've also considered Sigma, because they do make a 300mm f2.8 for my camera, and as I said, my IS is in the camera body, but I still doubt I can get tack-sharp images with it hand-held. Maybe someone here has some experience with that.
I'll see what I can do once I get my monopod and test.
But anything over 300mm, I presume, can't be used without a tripod, and a tripod is just too bukly and requires too much movment to adjust for the type of shooting I do.
For now, getting closer with a 200mm seems my best option. Besides, for me, getting closer than the average guy is what I enjoy most.