I put files that open in web browsers of my benchmark results at
http://www.math.purdue.edu/~lucier/bench-gambit-2012-11-06/
with a readme that's basically my original e-mail with the version that mzscheme reports (5.3) added.
I looked at the sources for fft.scm in the Gambit benchmark suite and in the Racket benchmark suite, and they are different, so it's not clear that the two sets of results can be compared directly.
Brad