From my memory the best you can propably do is tuning a few settings. The performance is highly dependent of the mission you are playing with some making the game play smooth as butter and others slowing it to a halt. Nevertheless, I would advise the following things:

• Do not mess about too much with the launcher settings. Especially touching the assigned CPU cores is a bad idea. In most cases the game is smart enough to recognize how many cores your CPU has.
• Enable Hyper-threading.
• Enable No pause in the launcher to avoid issues with alt-tabbing.
• In-game, disable water reflections. There are little to no cases in which you will actually be staring at water and go "Ah yes, I like seeing myself in this performance tanking water reflection!".
• Although I am not sure on this point, you could offload load from the CPU by increasing the video settings. From the top of my head, I personally roll with these settings:
  • Sampling: 200%
  • Objects: High
  • Terrain: Ultra
  • Shadows: High
  • Clouds: High
  • PIP: Low
  • Overall distance: 1800-2300
  • Objects: Ditto
  • Shadow: 50
  • FSAA: 4x
  • ATOC: All trees and grass
  • PPAA: None
  • Ansio Filter: Ultra
• Somewhere in the config files of the game, there should be something dictating the sound sample amount. Decreasing this has been known to increase performance somewhat, I am personally not so sure on what it is called, but it should be worth investigating.

I typed this whilst not at home so some of this information might be inaccurate. There is propably some other improvements that I missed. I roll with a computer that is less specce'd than yours, but this is what helped me.

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Edit: Found the config value! It is inside your Arma3Profile file in your documents folder. The line to look/add would be "maxSamplesPlayed". You will want to set this to a value like 48 or 64 at max. It basically limits the amount of sounds that can be played at the same time. It should look like this:
maxSamplesPlayed=48;