I'm hoping this group will share their thoughts.
Let me set the stage...
I have an opportunity to buy a Nikon 600mm F4 (edit from orig where I said F2.8 - sorry) AF D ED AF in almost mint condition, case, cover, and an internal circular polarizer for about $3,500 US.
In the bag I have a 300mm F4 AF-S ED, a 70-200 F2.8 VR, a 1.4 and 1.7TC and other shorter lenses. I shoot with a D2X.
Okay, why do I 'need' this lens? I love to shoot birds, especially in flight, and other dritters (bears, deer, wolf, etc) and the 300 doesn't quite reach. With the TC almost, but then I drop to F5.6 or less and can't get a quick focus lock. I've rented the 400 2.8 and it works really well for closer stuff, but not always enough reach. ALSO, I plan on moving to the D3 (or D3xyz ) eventually which means I loose the crop factor.
I am also considering the 200-400 but don't think I can come close to the same price, which will keep me from the D3 for quite a while ($).
Do I jump, wait for the 200-400, wait for a chance at a 600 II or other options? I know this lens is a couple versions behind, but is that a reason not to?
Let the suggestions flow... and thanks!