Did you mean 300 isn't enough or 400 Rob? I think 400 is about the best overall. Obvious there are advantages to 500 etc., but 300 is almost not enough gun for average wildlife shots that aren't park animals.
I have found 400mm to be not quite enough for the pic I want Bone. I haven't tried it with the 1.4x yet so don't know if that would be the difference or not

. Right now I have to crop the full body pics I get with the 400mm to get the shot I was looking for in the first place. I think the 400/1.4x combo would be just about right for most of the shots I am looking for. That being said, the 600mm was a joy to use especially when we added the 1.4x to it, I was getting clear shots at 840mm

I really dont want to spend $9,000.00 on a lens right now though that why the 400mm DO is on my list.