I get around 25 - 35 FPS in ArmA 3 when my friend, who has a less powerful pc, gets around 60 fps. He is on higher settings than me, here are my and his specs:
Mine:
GTX 970
Intel i5-4670k
8 GB RAM
His:
GTX 670
Intel i5-3470
8 GB RAM
What would cause my pc to run worse this game worse than...