It said around 2200 errors, there were artifacts on the screen.
I have overclocked my card from 715-850, memory from 1300-2200, could that be the cause?
Yup. Clock it to stock and run the test again. Make sure there are no errors at stock speeds.
You will probably have to increase your voltages to get the 850MHz speeds. Are you sure that is your memory speed or you Shader clock? The stock memory clock is 900Mhz, or 3600Mhz effective (quad pumped).