Double check your overclock. MSI Afterburner (and others) will not report the true clock of the GPU Core. Mine is showing 1359 on MSI Afterburner, but GPUZ shows a boost clock at 1290Mhz. The GPUZ reading is the true speed of the core. I can push the GPUZ reading to 1302Mhz but it does not last more than an hour or so before everything fails and Direct3D crashes. The differences in clock will result in the 5-7hash/s discrepency we are seeing here. I bounce between 199-203Khash/s but as I said before I sometimes dip to 150 for unknown reasons.
I think GPUZ is associated with TechPowerUp, so you should be able to find it via search.
What i posted earlier were the GPUZ readings. Anyway i ran some benchmarks for several hours and it seemed stable @1293.4 core and 1701 mem, but after about 7 hours of mining this night my rig crashed. Unfortunately i didnt run any diagnosis sofware except for GPUZ to check the temps, as i thought its stable after the benchmark results :/
I went back to 1280 core and 1700 mem for now, as i dont have time to tinker at the moment. With -l K95x2 -i 0 -H 2 it nets me ~188-190 kHash/s, still better than 160 kHash/s...