Parallel FFT on Xilinx FPGA
I think you could have been answered more directly.  There are many ways to accelerate FFT rate by using parallel structures.  A lucid and brief article is found at 

http://www.synopsys.com/Company/Publications/SynopsysInsight/Pages/Art1-fpga-signal-processing-IssQ1-13.aspx?cmp=Insight-I1-2013-Art1

or just Google "parallel FFT cores"

You will find effective rates of up to 8 Gss available on a V7 easily.