Yo can be fine with that psu, but 40W for 6970 is absolute bullshit. IT eats a lot of power, i had one once. No metter what cooler you use. Also be carefull with aftermarkets. Although they cools gpu itself very well, vrms will go very high on temps. That is critical for your stability. Also you may be using low intensity with that 6970, give us a screenshot where it shows how much it can mine and temps too.
The Arctic Extreme comes with heatsinks for the VRMs etc, I guess that would take care of them? Certainly upgraded treatment than when the stock cooler was installed.
I've taken some screenshots with some info on the 6970. You're welcome to comment.