Yea I have weight issues with my supertele's. I don't think it is an age issue, it would have been heavy packing the gear around when I was 30 years younger as well.

Somewhere I had read that the weight of the new 200-400mm was going to be in the 7 pound range. About the same as the 500mm F/4L. But nothing else has been said about the 200-400mm in a long time. If that is the case you are not going to gain much weight wise. I doubt we see one in at least a year.

+1 for Daniels comments about the 300mm. I have been thinking about selling my 300mm F/2.8 and trading up to the new version for the reasons he mentions. He didn't mention it but he is referring to the new 2x III not the II version.

Also Daniel, did you intend to link a 300mm F/4 comparison or a F/2.8 comparison?