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.