Wrong place for Z1000 vs 7520 discussion. I already compared them extensively over a year ago in the relevant Z1000 threads (twice!). Go find it if interested.
7520 frequency response can be found, but is harder to locate.
I had the 7520 for about a year and the Z1000 before then. I was praising the 7520 as my ultimate closed-can when it was pretty much being ignored on Head-Fi early last year. Now there is a much stronger following and even an active thread dedicated to it.
Given all this I prefer the FSP (I had them both together recently), but I would say the 7520 is no slouch either. The Spirit Pro pretty much redefined the word "neutral" for me. I hesitate to use that word now for any other headphone. I've been recently calling cans "balanced" if they have just the right amount of bass, mids, treble, instead of the word "neutral". I can still call them "linear" or "even sounding," but not "neutral" as I now know what the heck that sounds like and nothing really sounds like it other than the FSP. (2 others probably exist in the form of the Paradox and UERM, but I have yet to confirm this).