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There is no perfect loudspeaker, period. 45 based amps are sweet. The main problem is their very low output.
The challenge with high efficiency loudspeakers I've found is that they typically lack lower bass but do add various colorations (forward, nasal midrange is common). Crossovers suck power, yet single driver designs almost uniformly lack lower bass. Large extended range drivers are more efficient but the prevailing whizzer cones are simply mechanical crossovers. Yet without a whizzer cone larger drivers will "beam" higher frequencies.
Klipsch are quite efficient and traditionally (their classic models) are voiced for tubes, but their efficiency is over-rated, lack deep bass, and frankly can't compete sonically with modern designs. Even large reinvented classic designs sound better if fed more than a couple of watts as the amp can provide a commanding grip on the driver(s). Decades ago flabby tube bass was paired with such bass weak loudspeakers to achieve a synergistic mix, but that is just overlapping two colorations, which makes everything sound like those colorations.
Once upon a time tried to warm up to small tube amps, but being a "speaker guy" never could find an acceptable loudspeaker to match up. So I bailed out of small tube amps. Your best option may be to look for medium sized, as efficient as possible, extended range driver loudspeakers and add subwoofers. Floyd Toole and other noteworthy acousticians suggest multiple subwoofers carefully placed around the room to tame inherent in-room bass peaks/dips anyway.
