I think that most speakers, high efficiency or not, sound better with good tube amps than solid state, provided the amps are not pushed very hard. But, with many low efficiency speakers it really is hard to run them in a low-powered amps sweet spot if one listens at fairly high volume. I personally don't like most high-powered tetrode and pentode amps, the exception being OTL amps.
High efficiency speakers allow one to better exploit the advantages of tube gear, but, they can make the best of solid state gear as well.
I have heard my system with the First Watt J2 amp and I liked that amp a lot. The J2 delivers clarity, natural timbre and a grain-free sound. It does not quite deliver the enveloping soundstage of a good SET amp and notes don't quite give the impression of blooming into space and decaying naturally like a SET amp, but, the J2 is still good in this regard. The slightly hard edge to the initial attack of notes gives it away as a solid state amp. Still, I think it is a VERY good amp, particularly considering the price. I wish there was some way to hear their SIT amp in my system (the friend who bought the J2 and lent it to me for a week is not likely to buy another First Watt amp).