This was my unscientific test with the 14-24 vs the the 16-35. This was about a 200% crop (possibly more, not got the full sized images anymore) both at f4. The 14-24 is better than the 16-35, but does not blow it out of the water, the 16-35 is a terrific lens.
Image 1. 14-24mm Image 2. 16.35mm