It seems you mostly intend to shoot birds, so you need to consider how much you really need the shorter focal lengths, 400mm is really too short. I would say the 600/4 is the best choice.
I shoot a lot of lizards, though, too ... snakes ... as well as butterflies and insects that are beyond the reach of a macro lens.
If you need to cover the shorter focal lengths, maybe the new 200-400/4 if it's affordable, or the AFS 300/2.8 + 1.4 TC. The 300 has not been upgraded to Fluorite glass (yet?) but is still one of the top performing lenses, and is definitely more "luggable" than other options.
I already have the 300 f/2.8 VR II and it is indeed a superb performer. However, I
always have a 2x TC III on the end of it.
(I would like to get the same reach, without the image-quality hit of the TC.)
While quite satisfied with its performance, it is very heavy, and (more importantly), it is front-heavy, and not well-balanced.
I have read reports from people who state, although the 400mm/600 mm are physically heavier ...
they are balanced better ... and consequently don't
feel as heavy as the more primitive G design (even the 300G).
If you don't want/need 300mm focal length, and want the best IQ, how about 400/2.8 (with TC) and 800/5.6?. That gives you good options from 400mm up to 1000mm. A lot of cash any way you look at it ...
If money were no object, I would purchase the 200mm f/2 'Chubby', the 400mm f/28 FL ED, and the 800mm FL ED ... since I try to operate my "The Rule of Doubles" (or "Rørslett's Rule"
)
However (when I wipe the stardust from my eyes) ... my financial reality mandates I use the CV 125, the 300 f/4 PF (that I am selling my 300 VR II to get), and I'm pretty sure I'm going to culminate my decision with the 600 f/4 E FL ED.
Further, even if I won the Powerball, lol, I would NOT want to lug the 200mm f/2 'Chubby', the 400mm f/28 FL ED, and the 800mm FL ED around on a hike
But I very much
can handle 3 cameras, one with a CV 125, the other with a 300 f/4 PF (both holstered on a
Cotton Carrier), with the 600 f/4 E FL ED mounted on a tripod, slung over my shoulder