It is pre-overclocked to 1019 - (or 1097, not too sure what that really means)
So your 70mhz overclock still puts it to around 1.1ghz/1.15ghz.
I'm in a similar boat with my KFA2 670, except my results are even worse than yours. I'm putting mine down to the core tbh.
What software are you using to stress and overclock?