The speakers i would definitely recommend for that application are the JBL Professional JRX115 speakers, which can handle the power and will really do the job for you.

They have 15-inch woofers, which is what you need to deliver enough bass for that kind of large room full of people. Those Boston speakers will not even come close to handling the power or procucing the bass for such a large venue.

They are also designed for portability, so they can easily be moved out to the pool or the beach or the park as needed.

Amazon has a great deal on them right now; only $217 each.