Doubt Say and cameras cause any heavy load.
For those of you that want to experiment the effect, create a mission, put the player, save it and create a init.sqf file in the mission folder this way:
// Init.sqf
_log = "logic" createVehicle [getPos player select 0, (getPos player select 1)+1000, 0];
Sleep 2;
titleText["LOGIC saying alarm sound 1000 m away\nYou will hardly hear it", "PLAIN"];
_log say "Alarm";
Sleep 4;
_cam = "camera" camcreate [0, 0, 0];
_cam cameraeffect ["internal", "back"];
_cam camSetTarget player;
_cam camSetRelPos [2,2,2];
_cam camCommit 0;
Sleep 2;
titleText["LOGIC saying alarm sound 1000 m away with camera\nClearly audible now", "PLAIN"];
_log say "Alarm";
Sleep 6;
_cam cameraeffect ["terminate", "back"];
titleText["And the sound continues even after destroying the camera", "PLAIN"];
camDestroy _cam;
Sleep 8;
deleteVehicle _log;