That's hard to compare. Typically FPGAs are doing fixed-point math, so they can do more operations with less power. GPUs have traditionally done floating point. However, with the new Pascal architecture, certain cards (P4/P40) support 8-bit integer dot products, which give a massive boost in performance/W. It's still fairly high at 250W, but that's for an entire card with 24GB of memory. You'd have to compare that to an FPGA with that much memory on a PCIe card if you're doing apples to apples. Something like this is appropriate for comparison: http://www.nallatech.com/store/fpga-accelerated-computing/pc...