This can be easily done at stock voltage mem@150 core@840. You only need to replace cooling paste with Arctic silver. Usage is about 180... And I have tested your settings. I think you need batter kill-a-watt. I can't make it run with the usage that you reported last time... It uses about 120W+. If I remember correct you reported 85W.
That won't give you 391mh/s at all more like 330.
Right you are. I was looking at the wrong cart it is 940...