16gb of ram is no necessarly needed for a gaming pc but if you're gonna be doing a bunch of video/photo editing, or just having 100 things opened at once 16gb ain't needed 8gb will do you just find if you wanna save some money
You need GTX 970-980 and a quad core i5 but really an i7 if you want no problems with CPU bottlenecks in new big games like Fallout 4 and Assassins Creed syndicate.