[casper] Optimum PFB / FFT settings to meet timing

[Danny Price]

 Hi all, I'm trying to get the tute 3 spectrometer design running at 
250MHz, and am running into timing issues. The timing report suggests 
problems in the PFB and FFT -- does anyone have some recommended 
settings for the PFB and FFT (i.e. latencies etc), before I start adding 
delays haphazardly under the mask?

Also, any suggestions on a methodical strategy to meet timing?
Thanks
Danny