I'm running my S7s with EVGA SuperNOVA 1300 G2 80+ GOLD currently. So far no problems - but you'll need to get 2 additional splitter cables (PCIEXSPLIT6). There are more discussions about this on the forum here.
What batch do you have? Newest batches need more than 1300watts
I don't like the idea of splitting PCIe cables at all that is a no go for me. To spend so much on a miner then to do that seems like cutting corners. The best thing to do is have 220/240 and be able to use server PSU's.
If your stuck on 110/120 I would go 1600 EVGA that is like 400 dollars or so... which is pricy. I think if your serious really look into 220/240 in all honesty if you are thinking of S7's. Might look at Avalon 6's if your stuck on 110/120.