Dear Ozzysteve,
Thank you for the question, and our hearts go out to all of the flood victims in Australia.
I personally don't have any decibel levels that I can say these will go up to (some of the engineers at Bose who monitor this too may have an actual number for you). With that said, the same rules should apply, whether you are outside or inside, in terms of the number of people that one of these will cover. Obviously, without knowing exactly the number of people who are going to be showing up, I couldn't make a great recommendation, other than, just be prepared to have additional amplification if necessary. One of the L1's, outside should do well to upwards of 250 to 300 people, and you can double the amount of people if you an another system.
Perhaps other members of the Bose Live Music staff who read this, can respond in kind as well, perhaps some who have more experience using this outdoors.
Thank you and have a great day,
Eric-at-Bose