What would you buy

Watts are watts, doesn’t matter how they are derived.  The tube amps clip much more gracefully  and that is the reason they sound more powerful.

Then why did every one I tried sound more powerful even when driven nowhere near clipping? Three different solid state amps, 150 to 200 wpc, the best of which was the McCormack DNA1, but with less dynamism, mass slam and control, than 50 and 60 wpc tube amps. 

Its not true in every case. There are anemic sounding tube amps, just as there are POS SS. Its probably more the transformers than the tubes but whatever, point is, they are so not the same its actually kinda odd to be having an argument about it. I mean heck not even all SS watts are the same. They sure don't sound the same. Everyone knows it. Amplifiers sound different. Your position is simply untenable and only goes to show the hole you can dig yourself into when you rely too much on tech talk.

Vandersteens at 86 dB are admittedly at the bottom of the range of suitable speakers. But that's the bottom of the range of suitable speakers, period. Because sound is logarithmic, the power needed to produce it increases exponentially. Not linear. Its a big mistake ever to buy a speaker this inefficient in the first place. But if you have one, still its better to drive it with watts that sound good than watts that don't.

Tube amp sound is dominated by the output transformers- Roger Modjeski hand wound his own. The RM-9 used the Vandersteen 2 in development. An excellent match w and Vandersteen @clio this forum can connect you with what remains of Music Reference inventory.

as for efficiency, so often higher output is just trash - out of phase junk that counts as output.

Thank God we have millercarbon here to school all of us Audio no-nothings. Over 50+ years in the hobby and I still don’t know as much as him!   I am surprised there wasn’t a link to his system again.

stereo5"Thank God we have millercarbon here to school all of We Audio no-nothings.  Over 50+ years in the hobby and still don’t know as much as him."

It has been said that "It is never too late to learn" but please know and understand that millercarbon is often outright wrong about many of the "facts", claims, and advise he distributes here.

Also no matter which transformers coupled amp you choose do experiments with light loading the output transformers- so for example I use the 2 ohm tap on my RM-9 with Vandersteen Treo to great effect and keeps the amp in class A longer - the test is listening and light loading IF your levels can keep you out of clipping.

Roger M wrote extensively this and many related subjects- a search will reveal a lot of free wisdom- RIP Roger