That case is enough for Gtx 680?

and just changing air flow in your case may bring temps down a little but 70'C seems fine to me, my 560 hits those temps
 
70 is fine. My 680s in sli hit 65 at most but that is because I have 2 120mm fans blowing onto the cards and I have backplates on the cards too. A backplate may drop the temps by 2 or 3 degrees and it looks good. Might be an idea but realistically you are fine where you are.

When the card hits 70 is the fan at max speed? if not you could try and set the fan curve for the card so the fans kick in earlier and faster but you really dont need to.
 
70c is just fine, but if you want to decrease the temps put some fans on the side of the case as there is the opportunity. The case itself is fine i would say...
 
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