The 65% (or 1.5:1, or .65 ratios) are typical class AB specs. Some are higher, some lower. It depends on how the amp is made. Some people even suggest using a 50% efficiency rating in calculations. However, generally speaking, 65% seems to be the norm from what I've measured.
Class D usually reaches around 90% efficiency, give or take a few %. This is due to the fact that the output devices are either on with current flow, or off with no current flow. Since there is very little voltage dropped across the output devices (transistors, FETs) while current is flowing, there is very little heat. The only losses are usually created during the output device switching times, and maybe some power supply losses. The audio output is basically a high frequency square wave, with varying duty cycle (the ratio of "on" vs "off" time) proportional to the audio signal, which is then "filtered" by the subs coil and some amp components to create the audio signal (whew, that was a mouthful). As you can imagine, the quality of the filtering is somewhat dependant on the sub's coil impedance. Class D full range amps use much higher output switching, almost to the point of RF transmission!
