It can be more efficient. It depends on how sophisticated an emulator you are writing and how well the emulated CPU semantics match the host CPU semantics. For

It can be more efficient. It depends on how sophisticated an emulator you are writing and how well the emulated CPU semantics match the host CPU semantics. For a simple emulator of a CPU which is vastly different from the host CPU an FPGA will likely be much faster and lower power consumption, since although FPGAS are generally slower than dedicated silicon but they are really good at simulating arbitrary digital logic very fast, while CPUs are quite poor at it.