Is it a FPGA or an ASCI?
Hint: An sASIC would use less power than an FPGA. A custom ASIC would use even less power than that.
Spartan-6 LX150 is a 45nm FPGA. It gets ~20MH/W (and is very consistent among 3 different board designs). BFL chip gets 10MH/W.
Thus BFL chip is likely?
a) 45nm Custom ASIC (should have 4x to 5x the performance per watt)
b) 45nm sASIC (should have 2x to 3x the performance per watt)
c) nextgen 28nm FPGA (should have ~2x the performance per watt)
d) 45nm FPGA (should have similar performance per watt)
e) 65nm FPGA (should have half the performance per watt)