nice...
I'm in a country that is not very accessible to such electronics ("3rd world"), so I have to keep in mind a few factors when purchasing, since it will take while to replace items that go bad, if I'm able to at all. (eg if a PSU funks out on me can the other(s) handle the load of an additional miner)
Watts isn't a big deal where I am, cheap
So, 4 is an awkward number of miners to buy PSU's in a configuration suitable for that type of an over-build, without just ordering a 5th PSU to keep as a spare. If it were 6 miners, you'd say buy 3 1300's, and if one goes bad, 2 1300's can still handle 6xS3's.
However keep in mind it is possible to run one miner from 2 separate PSU's, as long as they are going to separate blades on the miner. So, what you could do, is buy four quality 750w PSU's (make sure they have 4xPCIe cables each), then you have plenty to overclock them all safely. Then, if 1 PSU goes bad you should be OK to run 3xS3 from 2x750w PSU at least at stock speed, or maybe with a small overclock.