Not quite slow, actually. And not power hungry. Altera top FPGAs have ~20W footprint with FLOPS performance about same as Intel Core i7 CPUs. I estimated that

Not quite slow, actually. And not power hungry. Altera top FPGAs have ~20W footprint with FLOPS performance about same as Intel Core i7 CPUs. I estimated that it might be energy-wise better to go to FPGA for at least some HPC workloads. Also, the speed difference between ASIC and FPGA designs are not in an order of magnitude. E.g., you'll have hard time optimizing your design for 2GHz and may even go to physical design for some components, while having 250MHz FPGA design is not a hard thing. I estimated that right now difference is two-to-four fold - 500MHz in ASIC, 100-200MHz in FPGA, with same development effort (Verilog/VHDL, no library specialization). Going physical in ASIC design means you'll stretch your development time by months or even years. Also you'll have to drop out some nice millions of dollars for CAD software licenses.