Well, this was one of the most interesting couple of days of lens research I've done for a while. The main problem with comparing these lenses is the utterly conflicting information that's been published on the net. Nothing unusual there per se but in this case the views shared were literally 50/50, especially when comparing the 17-35 to the 16-35.
I did finally come to a decision and a lens has today been purchased for delivery Monday. Many thanks to all who replied here.
The lens I've ordered is... the 17-35. In the end I had to dissect exactly what I'd use the lens for and how. Much of it's work will be landscape and architecture and for those two genres the lenses seemed fairly equal. IQ was seemingly similar, the 16-35 had the slight advantage of the extra 1mm width and VR, the 17-35 coming out on top with the extra stop. I'll discount build quality at the moment and even size as neither particularly effect the final image. What swung it for me was the extra stop. I'm fairly religious about using a tripod so VR was handy but not a deal breaker for what this lens would be used for. The ability to introduce a shallower DOF into images of people WAS a deal-breaker, though and that's what finally made me choose an older lens over newer technology.
A very enjoyable couple of days reading, however, and now I'm looking forward to enjoying the results!! Thanks again all!