Thanks to all who have responded.
I've bite the bullet and bought the 17-55 last week. Did a quick comparison with 17-40 on 40D.
- Better sharpness in 17-55 as per reviews. In fact at 17mm f/2.8 is even slightly sharper than my 17-40 17mm f/4.
- The 17-55 has vignetting at wide. Level is acceptable to me.
- Don't see obvious difference in terms of colours and contrast against 17-40.
My feeling is that on 4R prints, I won't be able to tell the difference in IQ of both lenses. But now have more versatility with 17-55.
Now need to get cir pl coz the one I'm using with 17-40 is not suitable. To thick for this EF-S lens
Happy New Year!
I've bite the bullet and bought the 17-55 last week. Did a quick comparison with 17-40 on 40D.
- Better sharpness in 17-55 as per reviews. In fact at 17mm f/2.8 is even slightly sharper than my 17-40 17mm f/4.
- The 17-55 has vignetting at wide. Level is acceptable to me.
- Don't see obvious difference in terms of colours and contrast against 17-40.
My feeling is that on 4R prints, I won't be able to tell the difference in IQ of both lenses. But now have more versatility with 17-55.
Now need to get cir pl coz the one I'm using with 17-40 is not suitable. To thick for this EF-S lens

Happy New Year!