Our sample board is now working at all the way up to 347 MHz. I was using a NTE NOR gate IC that I bought at FRYs, for both NORs (I wasn't using the one on the board). Looks like its fall or rise times are a little too much. I played around with a lot of capacitors. I finally modified the circuit to use the on-board nor gate chip for the first NOR and the FRYs one for the second. And now everything is working fine. The board is hashing very well at 300 MHz.