I run 20 rigs, 10 rigs are Sapphire rx 470 8g, and 10 rigs are Sapphire rx 480 8g, and all rigs are run with an eVGA 1300W psu.  I am dual mining ETH/DCR and run the DCR up to maximize output without hurting my ETH production.  That tends to lend itself to 1100W of power which is right at 10.0A of current on the 480 rigs.  Since I run 2 rigs off of one 20A breaker, I run a 470 rig and a 480 rig together because the 480's pull more power but can mine at a slightly higher rate and I control to a total load of 19A to make sure my breakers don't trip due to the swings in the process and power supply from the city.  All of my cards run a Mod'd bios and I run my cards to get 28.0 Mhs on the 470's and 29.0 Mhs on the 480's.  Depending on how you run your systems, I would recommend the 1300W psu since they are not much more expensive and it gives you some room on the DCR if you are only going to run one machine per circuit.  The more DCR you mine, the more power you will consume.  Plus, it will keep you away from the ragged edge of pushing you psu out of its control power factor.  Going up to a 1600W psu doubles the price and is only relevant if you have the room to pull that kind of power on your circuits.  Hope that helps.