OK, I have both lenses (and an older 28-135). Originally I was ambivalent about the 24-70 II and had it listed on the FM B&S forum, but retracted the sale. I decided to keep it for landscape work. My early testing showed the keeper rate was lower than I liked, probably due to lack of IS, and I had trouble accepting the cost. So I decided to dust off my old pre-IS shooting skills and practice a bit with it. Now I use both lenses. The 24-70 II is used for landscape and artsy stuff, while the 24-105 is used for environmental shooting and as a general walk about lens. Overall I really like the 24-70, it's one of the sharpest lenses I have (except for the 70-200 II and 200-400), and I'm using it more now for all work in that FL range. When I really need a wide angle landscape lens I do a 3 shot vertical pano and stitch. The 24-70 takes a bit of practice to use if you have become reliant on IS, but it's worth every penny I paid for it. Good luck with your decision.
P.S. As others have said, the resale value of the 24-105's has plummeted, so it's worth keeping as a backup lens.