Having never used the 24-70 f/4 IS I can't really speak its performance. But your post made me recall a couple of news articles from Bryan and probably more relevant here. So he is a fan.

About the only other thing I would suggest is considering the EF 16-35 f/4 IS. Depending on what else you have, something like the EF 16-35 f4 IS, 50 mm prime, and 70-xxx L is a very solid and flexible kit.

That said, there are a lot of times when the 24-70 II just stays on my camera and doesn't leave. All depends on what and how you want to shoot.