ah, the setting for bfgminer is actually
--set-device antminer:freq=0881
the default frequency is 0781 and you can try 0981
make sure you cool the device properly!
I'm putting in "--set-device antminer:freq=0981" into the manual flags field and then getting an error in the ASIC output window, "ANT 0: set_device is not implemented (trying to apply rule: antminer:freq=0981)", and then seeing standard rates (1.6 GH/s).
What am I doing wrong? I've been discussing it in r/bitcoinmining here:
http://www.reddit.com/r/BitcoinMining/comments/1uu3a8/antminer_on_mac_xpost_rbitcoin/cen5r77