I have used the 16-35, but not the Fisheye, but I can tell you for sure, they are entirely different lenses regardless of crop or full-frame. A straight comparison in terms of fields of view, look at the EF-S 10-22mm versus the 16-35L. The Fisheye has a much different purpose and field of view/distortion effect than the other lenses. The 10-22 isn't a full-frame lens but it is quite good when you stop it down. The 16-35 is definitely very good optically, and gets better when you stop down a bit.
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