Let me preface this explanation by first saying that I am NOT a professional when it comes to audio.
My understanding of sensitivity is as follows:
The sensitivity of a speaker is going to dictate how many watts of power you have to input into it to achieve a given level of audio output. If you can get to your comfort level by turning the volume control to say 40% with a high efficiency speaker and letís say 70% with the low efficiency speaker, generally, you will be introducing more distortion into the music at the 70% volume level. This happens because as you increase the volume and push the amplifier closer to its limits, a thing called "clipping" occurs as the sound wave is chopped off at the top. The amplifier, at its peak, is simply unable to deliver a clean (undistorted) sound wave unless it has what is called dynamic headroom (reserve power that is available when needed). I donít think the Stangís amp has this ability. How much of a problem this will be depends upon whether the amp you use can satisfy the demands of the music you will be listening to at the volume you enjoy. If your speaker is rated at 60 watts, your amplifier should, at a minimum, be able to provide at least this amount of power.
I guess the best thing to do is visit a local car audio shop and ask the pros what they think.