I have yet to join a multiplayer server that Arma 3 does not choke up and eventually settles around 5-10 fps.
I can make my own missions and they run just fine without any severe performance issues.
I have an older CPU and mobo, but it can handle every other game just fine on high settings, BF3, Skyrim, IL2:CoD, Rise Of Flight, Kerbal Space Program, etc.. The only two other exceptions being Arma 2 & PlanetSide 2. My new gfx card should be having -zero- issues with Arma 3.
Intel Core 2 Quad (Q6600) - 4 cores @ 2.4Ghz
6GB DDR2 (PC2-4300)
NVIDIA Geforce GTX 650 Ti 2GB DDR5