I think you're overestimating how finely engineered the bitcoin FPGA's would be. It's quite unlikely that the IO bus has been tuned to the barest minimum before affecting hash rates, I'd think it's much more likely that they were a) the easiest to acquire/use, and b) the cheapest. Odds are the low end FPGA's from the same manufacturer use the same bus as the high end ones, it's just a different processing unit and oscillator.
I'm
not worried about the FPGAs. Those are quality components. I am worried about
how it is wired on the board. If they chose to do it in the cheapest possible way, as you suggest, the boards will be unfit for almost anything but mining.
You aren't decoding video here, you're still manipulating strings. WPA has a key length of 256 bits.
With HDMI decryption you are decrypting live video at higher bitrate than the fastest Ethernet. I haven't mentioned WPA as anything but one of many examples. (And you obviously don't know anything about WPA either.) I want to know the limits of the different mining boards.