4 Ohm vs. 8 Ohm, what does it mean.....

Its way toooo general, Unsound.
You can grab an example on JM Lab Electra 926 where the nominal impedance is 6Ohm but it could be dropped down to 2.5.
My Totem Forests amps have a huge and resolving bass despite their tiny size and small 6" woofer. Their nominal impedance is 8Ohms and it doesn't go bellow 6. I was driving them with Pathos TwinTowers 35W/ch with enough loudness and clarity.
I might also generalize that speakers with lower efficiency have better bass while highly-efficient horns are only good for speach or voice...?

Rockead, it all depends on where larger current is drown. larger current is drown through the 4 Ohm and smaller is through the 8 Ohm. More resistance creates smaller current and thus creates "easier load" The heaviest load thus is a short circuit(0 Ohm in ideal case) when you connect with the uninsulated wire two binding posts per each channel of the amplifier(Don't do it at home 'cause you might damage your amp)

Nice article, Sean there is only something I wanted to add that SS amps in all logical sence do require deep negative feedback that increases an output impedance and thus creates an addtional voltage drop while in tube case the negative feedback is minimal. So there we have even more requirements for transistor(s) to pass higher current and certainly heat.