OsCollisionSound
From Open Metaverse Wiki
Opensimulator: Content Creators: Scripts: Functions: osCollisionSound
Opensimulator wiki documentation: http://opensimulator.org/wiki/OsCollisionSound
This function does exactly the same as llCollisionSound[1]. When an OSSL specific function duplicates an LSL one, it's usually recommended to use the LSL one (with the ll prefix) to maintain compatibility with Second Life. However, there may be occasions when you want to prevent your script from being ported to Second Life. In those cases adding an OSSL only function may be a low security way to achieve this.
When it comes to performance there should not be any difference between the two functions.