I bought a tube amp that had 4 ohm taps and speakers that were 6 ohm nom. Speakers had an impedance dip into the 3 ohm range. Ran them for the first year on the 4 ohm taps and they sounded fine. Then for kicks, tried the 8 ohm taps and never went back.T
...Until I bought Tannoys. Much better match for my amp.