Welcome to the forums mate.


John and Mike have covered things pretty well for you there so there's not a lot to add. However I will say that pretty much everyone that goes for the 17-55mm f/2.8 IS is very happy with it. It will be a very nice lens on your 40D.


I own the 40D and the 5D Mk II and started out with the 28-135mm f/3.5-5.6 as you have, when I upgraded to the 24-70mm f/2.8 I was amazed at the improvement in image quality. The 17-55mm will give you as good/ better image quality as the 24-70 on your 40D. It's not as rugged as the 24-70mm but it's probably a lot lighter (24-70mm is a TANK) and 17mm is reasonably wide on a crop body so will be better for landscape shots than the 24-70mm .


You are right though, it hard to pick between the two lenses - both are fantastic.


Hope this helps,


Ben