A few reviews at Audioreview indicate that some people prefer the sonics of the 3B over the 4B. If you look at straight power then the 4B will play about 3dB more than the 3B will so its not a helluva lot louder. I have owned both and can tell you that the 4B will provide more control and the strain has disappeared with my 1.5 Maggies vs when I had an old 3B. IMHO their repsective sonics are very much the same and will only be differentiated by how hard you drive them. I think that the extra $$$ for the 4B is worth it in the long run...
