Set Depth of Field option to low without significant visual impact.
Additionally you can turn off Ambient Occlusion and FXAA which affect the speed when aiming down sights.
"Error during Intialization:
ERROR: sound Bank failed to load cmn_root.Englisch. You have a Build Problem."
Set the lanuage of all three game parts (singleplayer , multiplayer and zombies) to your desired language and wait for steam to finish downloading.
Delete friends list until total is under 60, or add more friends until total is over 100.
Set Steam in Offline Mode.