I would prefer a newer design than old one since the technology travelsat thespeed of light . If I were in your situation I probably will keep my 17-40 and wait to get the 16-35L II sometime later. The 17-40L as I can see is a very nice lens but lack of a F2.8. I dont think it's worth it to trade the latest 17mm wide angle lens with something old, starting from 20mm but have a f2.8. It will also depend on which body you use, on 1.6x bodies 20mm is not that wide anyways.


I borrowed my friend's 16-35L and paired with my IIfor an comparison on B&W film during winter break. So far I have noticed clear corner sharpness improvement of the 16-35L II @ 16mm over the 1st generation. It's going to be more obviousif you use digital and pixel peeping. So my point is, lens will improve over generations, it's wise to save some money and buy the latest design, it will always be worth it.[]