What's the greatest bargain in SET these days?

Al, as Charles stated, I evaluated my deCapos in a 14 X 19 x 8 room with the dynamo and 3 other amps. I would suggest if rebbi is willing to limit peaks to about 90 to 92 dB he is probably going to be OK with the dynamo. I did not like my 500 wpc ss Cary amps with the deCapos at all. On the other hand, the inspire kt66 amp clearly ran out of steam. In terms of overall performance, wpc is one of many criteria as you know.

What troubles me is that rebbi needs to make a decision without benefit of an audition. I can't predict his assessment of the dynamo vs his Manley.

If the De Capo is easy to drive, that is actually more important than the efficiency rating. I have heard low wattage tube amps driving the very easy load 15 ohm Rogers LS3/5a speaker that is extremely inefficient (low 80's for efficiency) and the combination worked well even in a big room. On the other hand, the Wilson WP7 has a mid 90's efficiency, but even 40-50 watt tube amps would find that speaker to be a beast because of its very challenging load characteristics.

To me, the choice of the particular output tube being used is at least as important as the choice between single ended and pushpull. In either topology, the sound of the particular tube will come through and may be the difference between liking and disliking the result. In other words, if you happen to like a 300b SET amp, but, it turns out to not have quite enough power/control of the bass, consider a 300b pushpull amp in addition to looking for a SET alternative.

I haven't heard the alternatives you have been considering, except for the Art Audio PX-25. I like that amp. I actually prefer it to Jota (more delicate and beautiful sounding, though not as punchy), although the output power is quite low. I heard the PX-25 with very efficient Avantguarde speakers, and with much less efficient Spendor speakers and it is surprisingly capable for having a low output rating.

Good performance from a technical perspective and good sound are two different but related things.

Just keep in mind that any speaker will work with most any amp. Its just a matter of how well and how it sounds.

Rebbi's done his homework and pretty much knows the SWOT analysis at this point I would say.

I think there is a decent chance any of the prime candidates could work out for Reb given his goals. Is it a technical match made in heaven? I'd say no, but the end results might still hit the bulls eye, at least in this case.

Building the kit sounds like a fun project in particular.

"What troubles me is that rebbi needs to make a decision without benefit of an audition."

That's the problem.

He could always buy used initially to get a feel, then sell and buy new if needed/desired. That would be the risk mitigation strategy I would recommend from a financial perspective.

...or buy new with vendor provided support including a return policy for reasonable cost to the buyer.

Kit would be fun, but I would not know what to expect the resale value to be if it did not work out for some reason.

Tube gear in particular can be risky IMHO. I'd probably go with the product I like from a vendor with good support and reasonable return policy, if it were me.