Don't listen to this guy. I actually did a lot of research and built an arma specific pc that gets me 70 fps standard and still looks amazing with optimized settings.
get:
i5 6600k and overclock that shit.
air tower cooler
decent mobo
ddr4 ram with good speed. You don't need 16 gigs for arma since the engine is hard coded to only use 2 for some retarded reason. Get like 8 but if your going to play other shit then get 16