No reason to change the CPU and Motherboard. The 8350 is a very good CPU for gaming. The only change I would suggest would be the Power Supply. Let me explain it to you in short.
Power Supply is the most important part of the whole rig. If the PSU is of bad quality then there is a high possibility of it damaging your parts. And Raidmax Power Supplies are the worst quality Power Supplies, so you must replace the power supply
As
Soon
As
Possible.
Always remember PSU is the most important part of the PC. It converts the AC current from the wall to DC current which your parts can use. If the PSU is not good enough, then it would supply partial AC current which potentially can literally blow your parts. So, replace that Raidmax PSu with this one that I am suggesting below.
Power Supply: Corsair 860W 80+ Platinum Certified Fully-Modular ATX Power Supply ($139.99 @ Newegg)
Total: $139.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-12-24 03:28 EST-0500)
As for the problem with ARMA III, As far as I can guess, the CPU is not the concern. It might be a software thing. Since your rig can play every other game except ARMA III smoothly, so post it in the ARMA III forums, if they have any. Someone might be able to help you there. Try re installing the game, if that helps. But I can assure you that it is not a hardware problem. More like a software problem, driver, virus problem, etc.
Changing your CPU is just a waste of money if you ask me. 8350 is an awesome CPU, better stick with it. This would be my final opinion.