I thought the ATI cards already are quite effective with their stream processors.
An FPGA needs to be developed, and will only be produced in small quantities, making production costs higher.
I don't immediately see the added advantage over GPUs.

You should have put up some photovoltaic panels, 2 or 3 of 600 W each would probably do the trick, and run your computer off of it.
During the 25 years lifetime you can earn a lot of money. First digging for the last remaining BTCs, then earning your transaction fees.

Please elaborate on that and show us the calculation of how profitable it will be 

I would also be very curious to know this. 

Cheers