I'm looking to buy a new Zoom lens for my 400D. I have upto 400quid, but don't have to spend it all. I have it down to: Canon EF 70-200MM f/4 f4 L USM Canon EF 70-300mm f/4-5.6 IS USM AF It's to be used as a lazy zoom walkabout lens, I'm being drawn to the L lens for it's f4 at 200mm, but I wuold be losing IS and the extra reach of the 300mm. What are your thoughts? I should say that this is as an upgrade from my Sigma 55-200mm.