I have a more than acceptable pc(seen in pic) and I also am having this issue
I have tried adding launch parameters to utilize all cores but it doesn't seem to work with arma 3 ("-nosplash -skipintro -noPause -cpuCount=8 -high -maxMem=8192 -exThreads=7"). As you can see only 4 of my cores are being used and about 50% of my gpu and I'm getting 10 fps on ultra on the chopper showcase.....pc specs, FPS, core usages, and gpu usage in this pic
http://oi49.tinypic.com/s4am1g.jpg (1234 kB)
If anyone has a solution please share!