recommend entry-level high-efficiency loudspeakers

Hi,

I'm interested in building a shortlist of entry-level high efficiency loudspeakers suitable for use w/ lower powered tube amps, including single-ended triode setups. It's been a while since I actively researched audio gear and have never looked into high-efficiency designs in any detail.

I will define entry-level as absolutely no more than $1000 USD new but preferably speakers that are in the ~$500 USD used range.

Thanks for your thoughts.