I've found the 17-40 comparable with the 16-35 between apertures of f/8 - f/11. f/4 is a bit tricky though and best avoided unless left without an option.
I've would recommend that the OP should go through the image threads for both the lenses and (i) try to see the difference in IQ; and (ii) decide which lens has "mojo" that you are looking for.
I think that sums it up - if you are shooting primarily landscapes with a tripod or are doing studio work between f/8 and f/11 it probably doesn't matter which lens you buy - you may as well choose the cheaper option which is the 17-40. If you need to shoot at f/4, the 16-35mm is probably better. And of course if you want the subject isolation you get with f/2.8 or you want to shoot action, the 16-35 is probably your choice.
I haven't bothered with the 16-35 v1 cuz it's not sharper than the 17-40, v2 looks significantly improved.
I found the 17-40 has really poor corner performance at the wide end, mushy even when stopped down a lot. Performance varies with subject/focal distance. Seems worse at long landscape distances. But it does have a little more "something" when used on FF compared to the 10-22mm on crop, which I still do use occasionally.
FWIW, you can buy and try a used 17-40L and resell it if you don't like it and probably lose less than the rental cost.
FWIW, I've recently tried (by way of purchase) a new Tokina 17-35mm f/4
, hoping to find a lens that performed better at the wide end than the 17-40 f/4 L. (to use on my FF F-mount system)
I've only done some flat-field, close-in test photos and a few other landscape types.
It's the only lens whose FF corner performance, at least on the near flat-field tests, was absolutely abysmal. Pure mush at any f stop. Real-world images at normal distances were better but still poor corner performance until about 24mm.
Accutance was otherwise quite good in center and border areas and geometric performance was very good, holding straight lines very well with minimal distortion.
However, for the price, I'd not take the Tokina over the Canon 17-40mm f/4 L.
On F-mount it's a cheap enough option to consider.