Keep in mind that the chip that does the SHA256 hash is only one step in the overall mining algorithm. For each hash, you will have to transmit that data to some operation outside of the asic (those kinds of speeds may not work readily without engineering around some interelemental interactance issues). Also, it will take 'X' number of clock cycles to compare the output to some target value, and if it doesn't meet your target do some kind of data shift on the digest value, then resend that digest back to the hasher. Something like that. So, expect less than 18GH/chip. Finally, what is the cost fo one chip?

All that said, I'd still like to see what can be made with it.