Thanks for the nice wishes, Wayne!
Apparently the 2x TCIII works very well on the 500 f4, as Sar has sent me a sample pic that he took using this very same lens (as he knows the guy I bought it off) and it is as sharp and clear as if the TC wasn't even used! However, Sar has brilliant technique!
I will be giving it a try one day to see how well it works.
Like the 400, they are really in the real pro grade and they have IQ to match (as does the 300 f2.8). But, they are big and heavy and require support for any length of time. I will usually take my mono with me if I have thoughts of using the 500 f4.This is a lens you will no doubt own for some time to come, I know I love my 400/2.8VR and will probably own it as long as I own a Nikon F-Mount body and still shoot pics. I think you may find it a bit more challenging on a full day at the zoo, esp if you don't take a mono.
I have a Benro Gimbal head which I will use at some stage, but have not tried it in anger yet. Chasing birds with a tripod and Gimbal head is well, for the birds! I'd rather use a monopod, but will probably end up having to use it for some subject matter. Sar uses one of those heads that is like a swing and swivel system and he gets remarkable results.I'm wondering if you are now considering a Wimberley or other Gimbal, I know I have been for a while because even on the mono, moving the 400 around chasing birds overhead etc isn't easy..