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The only wide zoom that beats the 16-35 optically is the 14-24. The Sigma 12-24 and the Tokina 16-28 are worth considering, too.
I wouldn't get too concerned about overlap with your other zoom. That's more often a benefit than a drawback, and the sweet spot of the 16-35 is from 20-28mm. It's outstanding in that range, and will likely be much more satisfying there than the 24-120 (which is itself quite good).