8 Vs 4 ohms

Cford, The voltage at the 8 ohm tap is the same as at the 4 ohm tap, but the transfer of power to the speaker will be lower depending on the speaker inpedence. You are confusing the power consumption of the speaker depending on its impedence. The speaker at 4 ohms will consume twice the power of the 8 ohm speaker for the SAME voltage, if attached to the 4 ohm tap.
Tube outputs use transformers to match the voltage and impedence to the speaker requirements. Attaching a 4ohm speaker to the 8 ohm taps usually results in reduced power transfer and reduced damping, thus 'losser' bass. The opposite, results in stiffer bass, again with reduced power transfer. I find, that when in doubt, put the higher impedence speaker to the lower tap.
Bob P.

Eldartford, must be my dyslexia! Of course the voltage is twice as high on the 8 ohms as the 4 ohms taps, I reversed voltages with current to speakers or power or something in my mind! My comments about power transfer to unmatched speakers to taps holds, I believe.
Bob P.