Upload & Sell: Off
I traded my 16-35mm for a 17-35mm, mainly for the extra stop. Yes the 16-35 was a tiny bit sharper, and the VR is great. I think the 17-35mm has better focusing. Seems a little faster to me, especially in very dark situations (which could be because of 2.8 and brighter viewfinder). I know a lot of people have had problems with the focus motor in the 17-35 so I expect mine to get the problem someday, but so far it has been silent.
Overall I think it comes down to what you shoot. Landscapes, interiors, and static stuff I'd stay with the 16-35mm. For weddings, PJ stuff, the 17-35mm may suit you better.