Don, Some good points there, and I would recommend a 500mm f4 AF-S.
I went through a stage maybe 20 years ago, where I had a 400mm f3.5, then upgraded to a 500mm f4P ( manual focus lens. I sold the 400mm f3.5 lens and eventually sold the 500mm f4P for a 500mm f4 AF-I.
Of course,the 500mm F4 AF-I has been superceded by the 500mm f4 AF-S.
Reason I recommend the 500mm f4 AF-S, is that its a very good 700mm f5.6 with a TC14. These lenses are easily hand holdable, whereas, 400mm f2.8 and 600mm f4 are just that bit more difficult to hand hold.
I use my 300mm f2.8 AF-S, 500mm f4 AF-I hand held and only use my 800mm f5.6 (manual focus), supported by a Velbron Carbon Fibre Monopod. I do have a Manfrotto tri-pod and never use it.