FPGA power consumption

A client of mine is trying to build head mounted displays for the DARPA SCENICC program.

It is of course insanely ambitious--eye-resolution-limited imaging over the full visual field at 60 fps or so. It also has insanely ambitious SWaP (size, weight, and power) goals: 250 grams including battery, eyeglass or goggle form, power dissipation < 1W.

To try to make a sizing for that power dissipation, could you digital folks give me an idea of how much computing power I can get for, say, half a watt?

Thanks

Phil Hobbs