Quote: Question - is it worth paying a bit more and buying a 16-35mm
Lots of people have the 17-40 f/4L and few people have any problems with them. With such a short lens you can use quite a long exposure hand held, it's unlikely that you'd really need a f/2.8 lens in this focal length range (and, if you did, a prime would probably suit you better).
The extra millimetre at the short end of the 16-35 is insignificant but the extra 5mm at the long end of the 17-40 might quite often make the difference between having to change the lens and not.
I think my wallet would need an awful lot of convincing that the extra cost of the 16-35 was justified.
Add to that the fact that the 16-35 is considerably bulkier and heavier and, IMO, it's a bit of a no-brainer.