Running 2.5 watts out of the ft-817 to what is probably the world's worst antenna - a piece of wire running along some guttering about 2.5m up. With an earth, admittedly. The Elecraft T1 tunes it easily, but I am astonished at how well the 2.5W has got out. It turns out, i think, to be a better TX than RX antenna - a number of these stations can hear me, and only a few are heard by me but don't hear me.
By far the best DX here is RA0SX, who hears me but I can't hear him.
So why do we use such high power? I think there's an element of beat the competition. And, of course, nearly every mode will be much less efficient than WSPR.