I am in the market for a UWA lens for my Canon 6d. I am currently looking at these 2 lenses. Canon Price Watch has the 16-35 f4 for $1039 AR and the 17-40 for $619 after rebate. $420 is a big difference and price is something i need to justify to my better half if i choose to spend the extra money.
I am looking for people who have had experience with these lenses to give me some feedback on what they purchased and why.
A little background on me. Currently have a Canon 6d w/ 24-70 F4 IS, Canon 70-200 F4 IS. My previous camera was a Canon t2i and had the Sigma 10-20 UWA for that. I primarily used my UWA for travel and landscape. Mostly shot at f8. You can take a look at my Flickr page to see some of the image i took with that camera/ lens and the newer 6d.
Any feedback would be helpful and if anyone needs more information from me just let me know.
The research I have done online seems to suggest that 16-35 but I have always received such great information from this forum I thought I would ask the question here and get feedback from people who have used these lenses in the real world and not in a lab.

