Unfortunately your testing missed the real issue with Fallout 4 performance which is the CPU. Others have reported that the game is very demanding of high cores/threads and my i5-6600 struggles with this game. It turns out that the recommended i7-4790 is not an exaggeration. Your tests using the i7-5960x would never have detected the problem. Only a few have i7's so this is a bad idea by Bethesda.