I'm toying with upgrading my current main lens which is the Canon 28-135 IS F3.5-5.6 USM.
The one I have narrowed the search to is currently the Canon EF 24-105 F4 L IS USM.
The body will mostly be a 40D.
The question is - am I likely to notice a significant difference in image quality? Issues such as build quality, weather resistance etc are not so important given the care with which I use my equipment - but the bottom line is simply IQ. What does anyone think - will the difference be significant and noticeable?