I second marsupilami as I had to take my 16-35mm back and try another for my 1ds2 - it just wasn' t right. I tried a 17- 40 in the meantime but decided while it did some things well , and handled flare better in particular, that I needed the extra stop in brightness for focussing, I thought the 16-35 seemed a bit crisper in some areas too - perhaps colour wise. I thought Michaels test was very much in line with my own cruder results but after a year I'm very happy with it, but after looking at a friends results from the 17-40 on his 5d I'm sure I would have been hapy with that lens too.
Thank you Mr Dude and Christian for your replies. That seems to be sound advice to test the lens on my own camera body (5D). I usually buy lenses from B&H because they are considerably cheaper (including shipping) than getting them here in Brisbane, Australia. This time, I may have to spend the extra several hundred dollars but choose the best performer.
I have just installed DxO v4 on my system and have been very impressed with its performance. It does wonders with my 20D and 10-22, as well as on my 5D with a friend's 16-35. Unfortunately I currently own the 17-35 which is not supported. It seems like a good time to upgrade.
Thanks again for your advice.