I brewed a oatmeal stout on monday with a gravity of 1.070, I just took a gravity reading it is now 1.020. It did ferment at about 68-70 a little warmer that I would have liked. should I wait for air lock activity to slow before racking?
Yes, I'd wait at least a week on a beer that big. No matter what kind of yeast you used, you're 70% attenuated, so it's sure not done.