My current equipment is 50D (15mp) with 50 1.4, 15-40 4.0, 70-200 4.0 and 300 4.0 plus 1.4X. I process with PSE and print with Epson Photo R2880. I shoot just about everything from landscapes to birds. 300mm with 1.4 just does not have the reach or sharpness with either handheld and IS or with tripod. I just don't see a 500mm in my future due to cost. I am really getting into birds. Which would best suit this app--a new 5Diii with rumored 30mp and my current 300mm 4.0 or my current 50D with a 500mm 4.0. It can only be one or the other as buying both would put me out in the cold.