I have been racking my brain so much over this decision that I cant even enjoy my vacation. I already have a very old, (in mint condition) 80-200 f2.8L zoom. I am using it on a 5D2, so I dont have the reach that I need for wildlife or candid shots. Also I have serious vignetting unless I am above ISO 400 and f8. The lens is so old that Canon does not offer Peripheral Illumination correction for it, therefore I have to use post editing to erase the vignetting.
I am trying to decide between the new 70-300L or one of the 70-200 f4 with a 1.4teleconverter. I will be using it to shoot mostly travel, landscape, nature, wildlife etc... However, I still like being prepared when the occasional wedding/senior portrait occasion arises.