Canon 100-300mm - Depth-of-Field

Canon EOS 40D + Canon 100-300mm f/4.5-5.6 EF USM lens. There are plenty of these lenses on the secondhand market, and you don't need to pay much. The quality of the images it provides is pretty fair on a cropped sensor camera and at moderate ISO levels, stopped down a bit, and using the wider end, photographs can be sharp and vibrant. My copy has a bit of dust internally but adding contrast in post production soon sorts that out. Probably not a zoom lens to use at full telephoto and widest aperture in low light. But tell me one that is.
Shooting information: lens at 300mm. Aperture f/9.5. Shutter speed 1/500th sec. ISO 400.