I am pretty sure you would be fine. I am running a 6700k and a 970 OC'd to high hell on the S12 620W EVO and come nowhere close to 400W tdp. If you can stretch its nice but if it means skimping on other parts it is not worth it.
The 970 is a much more efficient card when it comes wattage demands. The 3xx line generally is quite consuming.