So @Phocal has started me thinking about this again. I have the 14-35f2 SWD and the 150f2 little tuna. The f2 maximum aperture is a real winner in a lot of situations. Darren Miles did a review of this lens recently - For me the downsides are obviously 1) weight, and 2) AF speed. The AF speed surprised me, I really had not expected the lens not to be SWD. The 150F2 which is pretty similar from an AF perspective is OK but not stellar. The 14-35f2SWD is really very good, good enough I don't notice the difference from a native lens. For anyone who has spent time with this lens I'd love to hear your thoughts.