You could look on the internet for the max wattage of both cpu and gpu since they're the main power suckers there. You don't need to, 750w should be good enough for those.
My suggestion is to pick one of these:
- Corsair RM750 X
- EVGA SuperNOVA GA or G5
- Enermax Revolution D.F.
- Seasonic Focus (or Antec, which uses the same components from seasonic)
These are the best psus you could have. All of them are available both 750w and 850w, with the 80 plus gold certification. I'm not saying that you need an 850w psu, but I think it could be better, in case of a future upgrade, to have more room without having to get a new one. Also you'd have lower temperatures inside the power supply and so its fan would spin slower, having a quieter psu.