Hi,
I wanted to point out that I often use ProcessExplorer by Mark Russinovich to look at performance ratings. I love it.
Just google ProcessExplorer.
You can see the different threads ARMA3 uses. ARMA3 seems to use only one thread. Sadly it doesn't show CPU performance per core, when viewing specific executables - only looking at the whole system. Just explore a bit, it has many uses.