I've read a lot of helpful information on the forum regarding the lenses I'm considering, and other people's choices, but despite that I am still having problems deciding on which would be most suitable (I suspect it's the thought of the expenditure) and so I would welcome your opinions. The core to my wedding/portrait system is a two body, two lens setup, which I find convenient and this minimizes lens changes. I like the flexibility of a full frame and a crop sensor arrangement. Initially, this consisted of a 24-105 f4L on the 5D and the 70-200 f2.8 L IS on my 40D. The problem is that an f4 lens is not always adequate in the dark situations we encounter in the UK, especially where there is some subject movment. (Incidentally, I prefer the flexibility of zooms, although I always carry a couple of primes as backups). Therefore, I'm not considering any f4 lenses (much as I love the attributes of the 24-105). My choices for a new lens are as follows: 1) Buy a 24-70 f2.8L for the 5D (and the 70-200 f2.8 then lives on the 40D). Cons: bulky heavy lens, no IS, slight gap between the two focal lengths, lacking on the ultra wide end should I need it 2) Buy the 17-55 f2.8 for the 40D giving me 27- 88 (putting my 70-200 f2.8 on the 5D). Cons: I'm worried that crop sensors will be phased out and I will be left with a very expensive bit of glass which I will be unable to sell or use; lacking on the ultra wide end should I find myself in a tight spot 3) Get a 16-35 f2.8L for the 40D giving me 26-56 (70-200 f2.8 on the 5D). Cons: not sure, feelings seem to be mixed on this one Your views would be greatly appreciated.