I have both the 400f/2.8 and the 600 f/4.
- they are both about the same weight
- the 400 is easier to take hand held shots due to the focal length and length of the lens
- both are awesome lens
- both work well with a 1.4
Realistically both should be used on a gimbal if going to be used for any length of time
I had a quick go with the 200-400 at a show - seems to be at least as heavy as the 300 f/2.8 so not exactly a lightweight, walkabout option. There are none to be had in the shops yet