Sometimes its a good idea to use a far bigger PSU than you need as it runs cooler, quieter and uses less electricity.
This. I learnt a long time ago that its always better to aim to have your psu running at 50-60% max capacity. This way, the fan barely operates in it and it runs cools and stress free.
If you calculate that you need 830W to run all your stuff, you are mad just buying a 850W PSU IMO as it means its going to running at 96% max capacity all the time.