Fredk,
For that live venue on my dock we were running 8 M80s with a total power of 5,200 watts. I had to put a 60 amp pony panel in the boathouse to power it all. Great party though.
The size of the space will make a big difference to the amount of power required. Every time you double the distance you are from the loudspeakers you lose 6 dB of output. It takes 4 times the power to make that 6 dB back up. As an example, if 90 watts per channel was sufficient but then you doubled the distance from the loudspeakers you would now need 360 watts per channel to get the same performance level.
