Jeff,
Playing for 400 to 500 people would never put a strain on the PAS, and in fact, it's unlikely that you would crank up the volume half way. It's not comparable to conventional speaker systems that must be cranked up to reach the other end of the room--it's totally different technology and deserves a try.
Good Luck,
Gary
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Travlin' Easy
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)