Sorry, I can't even start to talk you out of it. It is a simply awesome lens at 300mm and f2.8. With the 1.4xTC III it is the second best 400mm available (well, 420mm f/4), very fast focussing and very, very sharp. With the 2xTC III, its IQ is still excellent and it is has snappy focussing on the 5DIII, but slower on the 7D. It is a superb lightweight 600mm. I don't have any bad photos from it attributable to the lens, only me.
Go forth and buy it! And you too Neuro.