Ravi, speaker sensitivities are typically rated in db of loudness when driven by 1 watt and a typical in room sensitivity would be about 90 db. When driven by more than 1 watt, a dbW figure is used to show increasing loudness. For example, 70W=18.45 dbW, 80W=19dbW, 100W=20dbW, 140W=21.45dbW. These figures are added to the loudness at 1 watt, e.g. at 70W output level is 108.45db, at 100W it's 110db. Therefore the difference in loudness between 70 and 100 watts is only 1.55db out of an almost deafening 110db level. Doubling the power to 140 watts results in an increase of only 3db. To double the loudness level requires an increase of 10db, which in this case would require 700 watts. The point is that the difference in volume capabilities among typical amps and receivers is quite small and shouldn't be a major factor in the purchasing decision.
Incidentally, the setting of the volume control necessary to achieve a certain degree of loudness has nothing to do with how powerful the amplifier is. It's entirely possible for a more powerful amp to require a 1 o'clock setting for the same volume that a less powerful amp gets at 11 o'clock.
