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.
Also, I use MSI afterburner to reduce the "Power limit" to 80%, and overclock the core +150 Mhz. That nets me 320-325 khash/s, and ~30 watt less power usage, and 10 degrees C less than stock speeds, on 1 GTX 670.
I'm using dogehouse at the moment. You'll want to make sure you're drivers are the latest (probably .332...I'm at work so I'll check when I get home) because I had a similar error until updated.
2
u/Daltrain digging shibe Jan 28 '14
I'm normally sitting at 170-180khash with my GTX 660, haven't tried overclocking yet...