I also own the 17-55, and I, too, love it. It's a great lens, unbelievably sharp I think. For me, the f/2.8 has been indispensable indoors. I wouldn't be able to get the shots I can get if I had the 17-40 f/4, but only because I don't have an external flash. If you have one or plan on getting one, I imagine the 17-40 would be absolutely fine. Of course, you just said that you prefer to not use flash. So personally, I would go with the 17-55.


The 17-55 focal length is very useful, the IS is great.


Another advantage to the 17-55 over the 17-40 is the smaller DOF you will be able to achieve at f/2.8. Especially if you are doing portraits indoor, or shots of the baby, you can throw the background out of focus. Granted, that's just a comparison between f/2.8 and f/4....your 50mm f/1.8 would be even better at this.


Like this:


I'm sorry, I don't know how to post a hyperlink....here's my picture i'm talking about:


http://alex.shutterchance.com/photoblog/Tenderness_/2/


you'll just have to cut and paste, sorry!


alex