4-ohm setting with 8 ohm speakers

And yet, nobody has said a single word about reactance. This is implied when taking about impedance. Tube amps do not like capactive loads. period. I hope I got that right.
A 'flat' impedance curve? I've never seen one. If their are any crossover components at all, the speaker should 'swing' from capactive to inductive at some point, shouldn't it?
I think damping may be called on for Plato's above comment about 'looser bass' when using 4 ohm taps. With the whole amp OFF, how much resistance would I measure on 4 ohm or 8 ohm taps?

Other than that? Plato makes sense. Use whichever tap you like. I'd add that if the amp runs too hot while using the 4 ohm taps, I'd reconsider either amp or speakers.

Magfan, I think you read my comment wrong regarding me saying you'd get "looser bass with the 4-ohm taps." Perhaps I didn't make it clear but the 4-ohm taps (compared to the 8-ohm) would increase damping factor for tighter bass. Distortion would also be less using an 8-ohm speaker on the 4-ohm amp taps. I said the bass would be looser using the 8 ohm taps, and that the 8-ohm sound may be sweeter though less focused/precise, but that some folks might still prefer it that way.

What Plato describes regarding the bass is the effect I get when light loading my Music Reference RM-10 MkII. The loss of power is minimal as well, roughly 20%, so it runs at around 28 watts versus 35 watts. That's pretty negligible with my speakers since they are fairly efficient with a very smooth impedance curve.

Now my Music Reference EM-7 v12 amps can be configured for 3 ohm or 12 ohm output and I have tried both. Again, the lower output exhibited tighter bass and less distortion. However, with these amps I prefer the higher output.

And to complicate matters a little bit with what will likely be a footnote to the discussion, it should be mentioned that output transformerless (OTL) amps actually increase their output power into higher impedance speakers. Atma-sphere amps are the most well-known OTL amps although there are also OTLs from Tenor, Transcendent (incl kits) and others.

This makes Speltz autoformers particularly helpful with these OTL amps, although as the Speltz site testimony makes clear the autoformers can improve sounds with other amps as well.

Rrog, An example in ss amps is the Harman Kardon amp(s) in the Citation series years ago when hk abandoned their decent quality American-made amps for the Japanese-made lower quality amps after they bought Levinson. Not that there's anything wrong with Japanese-made per say. I think their 4-8ohm taps were to compensate for a less muscular amp that could not handle a 4 ohm load except at the expense of sound quality. And I think this device in ss is sometimes used to compensate for an anemic amp. I'm always suspicious when I see this device in ss, but I realize it has its place. My predjudice also comes from my dislike of switches which degrade sound quality.
I apparently didn't articulate my initial point very well because I surely don't have anything against using the tap that sounds the best as long as it doesn't cause damage to the amp. That's kinda the whole point of the tap. I don't have a technical background as some of you know, but I do understand in general impedence matching of amp and speakers. There is an optimum load for every amp. That is the point of the taps and the point of autoformers, a device used to find that optimum load. Lynne