The majority of us on OCN have power supplies which have way more headroom than we actually need (I'm a great example of this )
If in doubt you can add your specs into the PSU Calculator here to get a very reasonable estimate of real world power draw.
If you do get the XFX PSU, stay away from the Core series, my friend bought 2 of them and both of them have insane fan rattle. There's a warranty voiding fix for this, but you can avoid this altogether by picking up a different model.
And having an "Overkill" PSU lowers the efficiency drastically.