Thanks for the usefull comments...
Mark,
The way you describe to use the histogram is a bit diferrent then the way I have used it until now. I checked the image if it indicated blownout highlights (black blinking area's) and stopped down if needed.
Indeed the 24-105 shows some CA, but it is neglectible compared to the EF-S 17-85 I have owned. But I will have a closser look to RAW processing to improve image quality further.
Another thing to pay attention to (for me although ) is the vignetting of the 24-105 in the 24-35mm range. On occasions that the sky is over exposed, the vignetting causes the sky to turn into blue... During daytime I didn't notice it, because the LCD monitor is often hard to view in bright sunlight, but back in my appartment I saw it on my Epson P2000. In these narrow Italy citties (Siena, Florance etc..) you often have to strugle between blownout skies and shadows in the streets.
...but that makes life fun, otherwise it would be to easy offcourse...