As an Arma3 player myself, I used to have the same i5 4460 with a MSI R9 380, it wont work very well because Arma3 is a CPU intensive game, so the points you need to change in my opinion are:
- Go for Skylake system, Skylake 3.30 GHz - i5-6600 6M/LGA1151 $219.00, this CPU boosts to 3.9Ghz which will help you stay above the 30 fps in Arma3 Exile/Arma life etc
- 8GB Kingston DDR4-2133 KVR21N15S8/8 $30.00
- MSI B150 PC MATE (DDR4) USB 3.1 (LGA1151) Link Now in stock $94.00
This will increase 36$ on total price.
I also agree with changing the case as suggested by Anthony,
Edit: Some links that compares i5 4460 with i5 6600
Basic specs
http://ark.intel.com/compare/80817,88188
Users benchs
http://cpu.userbenchmark.com/Compare/Intel-Core-i5-6600-vs-Intel-Core-i5-4460/3514vs2310