[mihular]

850W is an overkill and will affect efficiency. I'd go with less power.

[Dylan16807]

If I go look up an arbitrary 850 watt supply (seasonic focus gold), it looks like it wastes about 10% plus 5 watts anywhere from 0-60% load. So extra capacity doesn't hurt that one.

[whatagreatboy]

Then you suddenly want a Nvidia GPU on the side and you need more power.

[wyclif]

Is 850W really "overkill"? I don't know. I suppose it depends on how likely it is you will expand and add devices.