the 16-35 gets bashed so much because of price premium. The 17-40 is pretty close at f/8 and smaller.
Samples vary just like with any glass. My 17-40 is decent, but mushy in corners even at small f stops. I rented 16-35 and I swear it was better in the corners, definitely below f/8.0.
I would hold out and see if anything gets released this year. The Tokina 17-35/4.0 i supposed to be really solid with nearly ZERO distortion!! to me, it looks close to both of your mentioned lens.
And lastly, there are two Zeiss 21mm Distagons on ebay right now for 1,485 OBO, slightly used. I am strongly tempted to buy one. If they will take $1,300 shipped i just might pull trigger. Used 17-40L anyone?