Overhead for dynamically loading assets.

I have a standalone game that is currently pushing computer limits due to everything (number of polygons, high res textures, and a boat load of colliders). The game is a single scene that is managed via scripts (LOD on polys + textures, disabling chunks of colliders and scripts that are far from the player, etc).

I'm about to implement sound and wanted to know the best way to do this. Currently our level design tools allow for the designer to put the name (string) of the sound in the inspector and a script will dynamically create the sound on another gameobject during runtime. The sounds can be played multiple times and there may be multiple sounds playing at the same time (usually 4+).

My question is, of the following, which would have the least overhead and best performance for a) initial scene loading b) runtime loading. Keep in mind that system resources are running scarce and every little bit of efficiency helps at this point.

1. Resources Folder (Resources.Load)

2. Streaming Assets (www streaming from local files)

3. Async scene loading (Application.LoadLevelAdditiveAsync)

Thanks for any help in advance... :)