I'm often speaking to an ex-soldier of a special forces-unit (not US Special Forces). He has a great experience in silently missions. He told me that they often had to use the knife or the garrote to eliminate the enemy silent.
Also there is a reason why its explained in the FM 21-150 (US Army Combat Training Field Manual) how you eliminate the enemy with a knife or a garrote!
BIS if you include SpecOps in ArmA2, please include their weapons too!