To follow up on this. I shot with a 35 L 1.4 this weekend. I haven't opened up the photos and took a close look at them, but from the LCD screen I could see they were clearer than the 24-70. So to recap on my experience:

1. Images were better. You could tell right away. Especially just the walk around pics of people during intermission or outside the venue.

2. The auto focus is way better. The 24-70 is already really good, but this lens can auto focus in the dark. Which makes me think this is a better lens for events when you are shooting at night (which most of the ones I shoot are at night.)

3. Its lighter and not as bulky.

4. Its 1.4. Can't beat that nice creamy blurred background look

Cons:

1. I love primes, but when shooting in crowded areas you have to move people out of the way a lot. But I'd rather have better images and just push people out of my way. Zoom is more functional.

2. On the 5D you get the tail end of barrel distortion. But this probably won't be an issue when using something like Lightroom that can fix that.

Overall, if you had to make a choice between the 24-70 and 35, I'd probably pick the 35. The IQ of this lens is really something. I kept hearing about it, but now that I can see it. I plan on shooting more stage performances with this.