My recollection is that by definition 1 dB is the threshold of the difference that the human ear can detect, and that 3 dB is double the SPL of 1 dB.
My feeling is that, while it is always preferable for a speaker to have a higher power rating, it does not necessarily equate to the quality of the sound produced. Now, a speaker with more dynamic range will have that quality as one advantage but it could conceiveably lose out on many others. As a personal example I never cared for the sound of Klipsch speakers as much as I did the Quad ESL 57s I owned. But your mileage may vary, especially if dynamic range is at the top of your list.
My feeling is that, while it is always preferable for a speaker to have a higher power rating, it does not necessarily equate to the quality of the sound produced. Now, a speaker with more dynamic range will have that quality as one advantage but it could conceiveably lose out on many others. As a personal example I never cared for the sound of Klipsch speakers as much as I did the Quad ESL 57s I owned. But your mileage may vary, especially if dynamic range is at the top of your list.