the 70-200 f4 l I'm sure has amazing iq but the lack of is does worry me. 97% of the time I don't use tripods, and I don't like to go higher than 800 or 1250 on my 40d. The winters in northwest europe are quite dark and dusk comes early.
As are the winters in New England. IS is helpful...as long as your subject isn't moving. But if you're trying to shoot a moving subject, IS doesn't help as much (more benefit at longer focal lengths, though, where shake is worse). The 4-stop IS on the 70-300L means you can handhold down to 1/20 s or slower...but shooting a person posing for a shot at 1/20 s will still usually have blur due to subject motion.
I suppose I am a little concerned about the bokeh on a 4-5.6 lens. Is it possible to get enough out of focus with a crop body at those focal lengths?
Depends on the how close you are to the subject, and how far the subject is separated from the background. In practice, it's aperture and distance to background that determines background blur, not focal length. For example, if you frame a full-length portrait at 50mm f/2.8, you'll have a certain DoF. If you take that shot with a 300mm lens, the longer focal length would mean shallower DoF, but you'd have to be much further away, and the longer camera-to-subject distance would mean deeper DoF which would exactly compensate for the longer focal length.
But, if you take care to allow good physical separation between your subject and background, you can get decent OOF blur at f/5.6.
