Forget about watts. You need to model the drivers you intend to use in a modeling program like WinISD Alpha Pro and look at the maximum SPL chart to see what they're capable of. And forget about SPL calculators as they're only accurate outdoors. Indoors room reflections make speakers work literally twice as well as a simple -6dB/distance doubling would indicate, so a -3dB per doubling of distance is a more likely scenario.
Bill Fitzmaurice Loudspeaker Design
The Laws of Physics aren't swayed by opinion.