If you are hosting a dedicated server running off a Windows Server 2012 machine, you will notice the server FPS always starting off a little lower compared to an identical server running off Windows Server 2008.
This issue has been present in both Arma 2 and 3 for a long time.
Idle server FPS with 1 player on 2012 = 47-48.
Identical server setup with 1 player on 2008 = 50.
http://forums.bistudio.com/showthread.php?171485-FPS-issue-on-new-Dedicated-Server