Sorry this has been asked before I'm sure. I'm about to get down to replacing stolen gear after finally getting close to (not quite) the insurance money. I previously had a 17-40 which I thought was a decent lens and increasingly used with my 70-200 f4 IS as my general purpose travel kit (recently adding a 100L IS macro), leaving the 24-105 at home.
I've been slightly tempted by the 16-35 as the price gap has reduced a bit and there is a decent cashback on both lenses in the UK at the moment. However, there are many opinions around that the image quality is essentially the same, the only advantage being the extra stop. Well that is nice for available light of course but with the high ISO performance of the 5D2 I can get by without it. It would mostly be used for buildings/streetscenes/landscape and looking back over EXIF data for my 17-40 images, they are mostly well stopped down. I know the 16-35 has an advantage in the corners at 16/17 mm up to about f8, but realistically, I'm going to be cropping the corners off anyway in correcting for the barrel distortion.
So I can't really see any compelling reasons to choose the 16-35 over the 17-40, for my uses. If I was doing weddings indoors in available light, the answer would I think be different. (Also, the difference in price is about the cost of replacing our broken dishwasher!).Relative to the Zeiss 21, or 17/24 TSE lenses both are in the same ballpark.
Anyone want to advance a view that the IQ of the 16-35, overall, is a significant step up from 17-40?