I really like my 100-400mm on my 7D - very sharp. Based on the reviews, the new 70-300mm L looks like a great lens. But, thekingb is right - sometimes, you need the extra 100mm. With the 100-400mm and 7D, I shoot birds frequently, and I often still find I need to crop the images (which has me considering the 500mm f/4L), so for that use I would definitely not be willing to give up the 100mm (in fact, my first white lens was the 300mm f/4L IS, and I went to the 100-400mm for the extra reach).