I need to know a build for this also I can build it myself and I don't need a mouse,moniter,ect just the pc parts also I only have a $1,500-2000 budget
You can also add an SSD and place your OS and games in there for faster load times, I would go with a 840 EVO 256GB
Here are benchmarks for a single 970: http://www.anandtech.com/bench/product/1355
it's a super powerful card, and can be overclocked because it's great at overclocking
For Arma 3 you do not need a powerfull GPU , just a lot of vram and an high clocked intel CPU. and you need to turn down PIP , HDR, shaddows than you wil be fine.
The gtx 970 has a memmory issue, it can only use 3.5gb vram. I would go with a r9 290 4gb version , but i leave that to you