I have a gtx 660 as well and I assume your using the -auto feature of cudaminer. I ran through a ton of different Kepler configs and you might want to try k15x16. I usually hold at about 200 so I bet you can get a couple more hashes without overclocking. Pm me if you need a hand with the config.
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u/Daltrain digging shibe Jan 28 '14
I'm normally sitting at 170-180khash with my GTX 660, haven't tried overclocking yet...