Just edit the cgminer.conf file and set whatever freq you want.  I tried higher but had to lower it since the higher values either weren't stable or produced a lower hashrate.  Eventually I settled on 756 as the sweet spot for this unit.

As others have said about their batch 2 miners, the third board on my batch 2 miner just doesn't handle OC very well.  The other two boards seem to do fine with the higher numbers but that third one either doesn't hash at all or does so very poorly.  I have to limit the OC on the whole thing to accommodate that board.