According to [1], a high-end FPGA can do "AlexNet inference performance: int16 over 2,400 img/s, int8 over 4,500 img/s.". Plug in your favorite nVidia numbers and compare.
That seems odd - just the XCKU115-2FLVB2104E FPGA goes for $9000 on DigiKey.
Do you think TitanX has real time capability?