I bought this PC from Best Buy a few months ago, found it works pretty well on older games like Assassin's Creed II but starts to lack only in Brotherhood. Here is the the PC and here is my PC Part Picker List.
(please not that some of the items on the list are just place holders because they did not have the actual part that is in the computer...)
I am looking to upgrade to the NVIDIA GTX 970 ASUS STRIX edition and my power supply is 400 Watt ATX. I put all the specs into PC Part Picker and it says that the estimated wattage is 349 Watts for my PC after the upgrade. So, is 50W enough headroom for my upgrade? If not, how many watts would a decent amount of headroom be?