I have the 24-105 and had the chance to use a 17-40 while out in the Tetons for a day. Really liked it for the landscape stuff. I had been debating selling/trading the 24-105 for the 17-40 before leaving and decided to hold on to it. After using the 17-40, the debate is back on.
This focal length would really be used for landscapes, maybe the occasional daughter portrait and for walk around. I find that I grab the 70-200 for portraits inside or out, so the 24-105 really doesn't get used that much (except for when I go wider on FF).
Any of you used both and picked one over the other? Curious on opinions. Would also be used on a 50D on occasion but primarily on a 5d.
Imho, there is no better walk-around lens than the 24-105 (for FF, of course).
But since we don't know what exactly you do with your lenses and what are your requirements, it's all guesswork.
If it was me, I would sell the 70-200 and get the 100-400 (or the 150-500) and the 17-40. But, in my case, I don't need a fast lens and chances are that if I need something longer than 105mm it would call for 300-400mm+ rather than 200mm. I am sure many would disagree, but I find both the 70-200 range and the 17-40 to be very limiting, I wouldn't use either as a walk-around lens.