Hi bowerymarc,
Sorry that it took me a few days to get back to you.
I don't think overclocking the device would damage the device in any way. Actually, I'm surprised that the PLL was even able to lock to the clock when it was using the wrong predivider. I would expect the PLL to not lock and the device to just sit there idly.
Perhaps the unresponsive nature of the device is due to damage or loose solder joints?
A good test to see if the comm port and memories are alive would be to try reading back some registers you've written and check if the values match. Then, if you try to run a program, put a DC source in it connected to a DSP readback cell. You can write to the DC source and read from the DSP readback cell to see if the program is successfully transferring the data from one memory location to the other.