Scott, RMS (root mean square) is the power a speaker can handle continuously, so 400 is the number you are looking for. You might want to take a look at this article: http://www.prosoundweb.com/install/church_talk/primer3.shtml

"First, there's power handling capacity, usually defined by terms such as "Continuous," "Program" and "Peak". Continuous is the level of long-term average power accepted by the loudspeaker; Program is based upon a test signal that simulates a "real-world" program signal; and Peak refers to the maximum amount of short-term power the loudspeaker will handle."

-- José.