Faster per watt? certainly. Faster per the cost of the device? No way in hell.

Due to the more popular altcoin algorithms being heavily memory dependent, FPGA's have no real advantage. Sure they can crunch whatever little there is to calculate more efficiently but they still have to be hooked to a gpu style memory controller with regular ddr memory.

There are some exotic FPGA's with more advanced memory tech than DDR too but when it comes down to random read bandwidth per dollar, you just can't beat a modern GPU.