Portrait Zoom lens for Canon Rebel

I have read the reviews, but before I spend a lot of $$$$$ I want to get this right. I am looking at the Canon 24-70mm 2.8 L lens for in-studio and environmental portraits, and weddings.

I am looking to compliment my 100-400mm L lens. Maybe I just need to "justify" this, but your comments would be appreciated.

Here is an example of what the 100-400mm Imaging Stablizing lens is capable of. This was taken in a relatively dark church setting.

Thanks.

-Dave-