Check out Antec's website. They have a power supply configurator that will roughly tell you how much power you need based on the components in your system. Then you can search on newegg for a power supply that will give you some power headroom over what you actually use. Unless you are running multiple cores and multiple graphics cards, you will most likely be just fine with a solid power supply ranging anywhere from 380 to 500W.
That's plenty of power. I used a 380w for a while with my 3850 (overclocked with an OC E2160 too) 420 is plenty, they don't use nearly as much power as the 2900 they were based off of.
You are about to answer a thread that has been inactive for more than 6 months. If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.