Actually I think the same arguments were kicked around when 35mm camera started being used for fashion shooting. In that MF offers massive DOF control were as 35mm can itself at times be more limiting. I think it is one of the reasons for the drive for faster shutter speeds on 35mm cameras to help keep the f stop at a low number. But again you use ND as well. I cannot see in term of dSLR the size of the sensor making much difference in terms of weight. With something like the 5DMKII you can just crop back to give you a APS image. Example of this is the 7D (820g) against the D800 (900g). But looking at prices it would appear making FF sensors is a expensive business where as APS ones are much cheaper. So in that case it comes down to personal cost and choice. So I reckon if you can afford FF and you don't mind carry a dSLR you might as well get dSLR with FF on board. I'd like to see a FF sensor in a lightweight body with a EVF. I am hoping that Sony make the NEX9 like this. I reckon you could get the body weight right down to say 250g then with a long lens (400mm) the whole kit might go under 1KG.