For your 8 ohm speakers efficiency=sensitivity. Driven by 1W they will deliver 86dB sound level. 30W (30:1 ratio) should give you about 15dB more resulting in 101dB. It should cover even symphony orchestra (EU directive limits level to 85dB in order to protect musicians).
Efficiency is defined as loudness at 1W power at 1m distance in open space. Since average room is not an open space (sound is amplified by reflections) it can be assumed to be the same in whole room (unless room is very large).
Efficiency is defined as loudness at 1W power at 1m distance in open space. Since average room is not an open space (sound is amplified by reflections) it can be assumed to be the same in whole room (unless room is very large).