[astrodust]

They're slower in terms of clock speed, but they're not slower in terms of results.

You can do things in an FPGA that a CPU can't even touch, it can be configured to do massively parallel computations for example.

If Bitcoin is any example, GPU is faster than CPU, FPGA is faster than GPU, and ASIC is faster than FPGA. Each one is at least an order of magnitude faster than the other.

A GPU can do thousands of calculations in parallel, but an FPGA can do even more if you have enough gates to support it.

I haven't looked too closely at the SHA256 implementations for Bitcoin, but it is possible to not only do a lot of calculations in parallel, but also have them pipelined so each round of your logic is actually executing simultaneously on different data rather than sequentially.