Arma 3 Upgrades

Solution
The PSU isn't enough for 2 X 970's I suggest atleast a 750w. That power supply may have a hard time even with one GTX970.

PCPartPicker part list / Price breakdown by merchant

Power Supply: Antec HCG M 850W 80+ Bronze Certified Semi-Modular ATX Power Supply (£98.99 @ Scan.co.uk)
Total: £98.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-10-31 23:46 GMT+0000

On ARMA 3 I suggest lowering these setting to check which part is cause the lag.
Working out the bottleneck for the CPU you need to lower the following settings: Objects, Terrain, Overall Visibility, Shadows – set to, Standard(forces shadows to the GPU).

Test the GPU you will want to...
The PSU isn't enough for 2 X 970's I suggest atleast a 750w. That power supply may have a hard time even with one GTX970.

PCPartPicker part list / Price breakdown by merchant

Power Supply: Antec HCG M 850W 80+ Bronze Certified Semi-Modular ATX Power Supply (£98.99 @ Scan.co.uk)
Total: £98.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-10-31 23:46 GMT+0000

On ARMA 3 I suggest lowering these setting to check which part is cause the lag.
Working out the bottleneck for the CPU you need to lower the following settings: Objects, Terrain, Overall Visibility, Shadows – set to, Standard(forces shadows to the GPU).

Test the GPU you will want to lower these settings: FSAA, SSAO, Shadows – set to low(forces shadows to the CPU), PPAA Resolution / Sampling.
 
Solution