Actually, a quality 450W unit is sufficient for that rig. The wattage of the PSU will not affect performance. A GTX970 should be able to max most if not all current games on a single 1920x1080 display.
In any case, quality is the key attribute of a PSU, not [claimed] wattage. I'd get one built by Seasonic (their own, XFX, some Antec), Delta (Antec Earthwatts), or Super Flower (Rosewill Capstone, Kingwin Lazer, EVGA B2 or G2).