4 ohm or 8 ohm tap on old tube amps?

I think user name KT88 gives an idea of what happens in this other thread.

07-22-12: Rrog
Hifitime, KT88's post sounds impressive, however, VTL and Manley Labs have always provided only one output on their amplifiers set at approximately 5.5 ohms for the best sound with the majority of speakers.

Yes, they did it by choice. However, you can see some significant differences in this test done by Stereophile. It really shows in the power output differences between the 4, and 8 Ohm output power measurements. Without the other impedance taps, we'll never know how it would compare sonically, to its one fixed output.