What is the best high efficient monitors under 1K?

Parts Express has a system using the Dayton Audio RS series drivers at #580 or a used set of Coincident Triumph UHS.90/92db/watt respectively.

Von Schweikert VR-1

Agree with both of the above recommendations, Coincident Triumph and Von Schweikert VR-1.

My buddy and I spent a couple of months going around and trying to find a sympathetic pair of speakers for his very low powered amp, and they were the only two that cut the mustard. Different tonal balances, however. The VR-1 are more clear in the treble, while the Coincidents do a better job with the bass (especially) and mids, not that the VR-1 mids are at all not recommendable. The Coincidents sound more open and spacious, though.

You can't go wrong with either, the recommendation goes to one that meshes with your preferences best.

Might also want to try the Omegas...