Just wondering if anyone has any experience using the 400mm 5.6L with a FF for bird shots. I currently have a 70-300L and use it with a 7d for birds. I have been pretty happy with this, but I would like to use my 5d3 for some bird shots and 300mm just doesn't cut it. Anybody use the 5d3/400 5.6L combo? It sounds like it is light enough to hand hold, so that is good. My main question is how big a deal the lack of IS really is. One of the bigger IS whites would be great, but not in the budget since I mainly do landscapes. I guess I am looking for a solid, value 400 and wonder if this is it or if I just should stick to what I have right now. Any thoughts or advice appreciated.