Looks like I would need a 1300+ watt PSU. But I have read guys running a 6*1070 rig with 800W psu.
A single 1300W PSU costs a lot compared to 2*700W PSUs. But then I don't have any experience in mining.
In fact, You can under-volt your cards. Like I said before that I use safer calculation, so I'm using TDP.
Then, tried it! only with tried you will know, and you'll get an experience.