The largest outdoor venue I've done using the Bose L1 Standard system was Aberdeen, Maryland Municipal Park, which measures about 600 X 800 feet. I was in a raised pavilion that is about 3 feet higher than ground level, which provided some protection from the sun. I still had to shade the keyboard's display with a homemade hood, through, just to see it. I never turned the remote's master volume above the 11 O'Clock position and people were dancing at the opposite end of the park. I did a 1-hour concert there for the county's Department of Parks and Recreation, and they invited me back every year for the next five years.
I wouldn't hesitate to do most outdoor jobs with a pair of Bose L1 Compacts, but of course, much of this will depend upon your audience and the type of music they want to hear. If they're hard-core rockers they tend to love ear-bleed-loud and distorted.
Good Luck,
Gary
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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.)