I'm not familiar with the Tamron, but the Nikon 17-35 is a great lens. I used it routinely with my D200 and now with my D700. You won't be sorry, but of course how much you use it depends on what you shoot.
I'm sure you're right about the Nikon, but this isn't the time for me to spend 4 digits on a lens. I just bought DS-160s, $2K in car repairs, etc. So today I went out and bought a NIB Tamron 17-35 f2.8-4.0 for a mere $200 from a place that is closing up. 77mm filter size, so I can use the same +2 diopter I already have for the Tokina 11-16. Can also use the same zoom gear as the Tokina, and the Ikelite port body for it is a very useful 5510.16. Probably a lot lighter lens too.
I don't pretend the image quality will compare with the $1500 (or whatever it is) Nikon, but I also don't want to pretend I'm anything but a duffer trying to get some nice photos. I could get a LOT better before I need that quality.
It's funny though -- I can get fussy about macro. At first I thought i was clever to get a secondhand Tamron 90mm, and it IS a very sharp lens. It wasn't long before I was wishing I had bought the Nikon 105 (will do that someday). I got tired of the lens hunting to autofocus with blennies and gobies...
BTW, loftus, that over-under shark photo you posted in the thread about the Tokina FE with teleconverter on FF... I love that shot. I'd be on cloud nine if I ever took one like that.