I'd also just like to make clear that an FPGA has not been chosen for this board in hopes that by the time things are ready, a chip other than the Spartan 6 might be cheaper or perform better. There are, however, candidates.

I am not planning on using a 28nm chip, either, unless something really, really unforseen happens.

In fact, so that there are no miscommunications, the current candidate FPGA device for Nanominer is an XC6SLX150.  That is subject to change.