It seems to me the engine generally need optimising though. Even in SP mode, even though I get a fairly playable frame rate most of the time, I get occasional graphical lag, mainly when zooming with scope or binoculars. I'm using an i5 3570k and GTX 660 which I thought should be able to handle Arma 3 on ultra in SP very well.
And thanks for clarification regarding servers and dev build. Hopefully this can be put back to normal soon.