Best Values In Speakers To Pair With Coincident Frankenstein MKII Monoblocks?


A good friend who I have gradually been introducing to quality audio for the past few years has decided to start by putting together a SET system, based on demo's, attending both Axpona and Rocky Mountain this year, with me. He started his new system by purchasing a mint condition pair of the superb Coincident Frankenstein MKII mono's, and we are now currently attempting to match these amps up with a suitable pair of, at least somewhat reasonably priced, suitable high efficiency  speakers.

His room is 13.5x15. We would appreciate any insight, recommendations and suggestions, from you, of speakers that would pair very well with the Frankenmsteins. His budget is $5k or under for a used pair (to maximize his budget). Any speakers within the budget, that you have heard working well with these amps, is fair game, excepting any speakers made by Coincident. I would appreciate it if those are excluded from the discussion. Most are too expensive anyway, and there are other reasons for the exclusion. Not that Coincidents aren't fine speakers, but they don't fit into our scenario. Thanks for any help with this, it is greatly appreciated. 
nightfall
I would highly recommend Audio Note you can find used J’s and possible used E’s for under $5K. Easy to drive and designed to be paired with low powered tube amps. I have a pair of J’s myself and love them a very natural organic slightly warm transparent sound. And great tone!
The Klipsch Heritage series come alive with 3-8 watts of SET.  I use the La Scala with the same Frankie-Mk-II with outstanding results but in a room of your size the smaller Heresy-III or Forte-III would be outstanding.  Note I'm not really a "Klipsch" guy and use various single driver speakers that I rotate in & out of my system but I must say the Coiencident Frankie does match with the Klipsch Heritage line well.
They don't come up much, but Coincident super or total eclipses are beautiful matches. Some other Coincident speakers aren't quite efficient enough. I had Frank's and SEIIIs and loved it so much I bought Coincident PRE's. Unfortunately the Frank's just don't have enough power for those speakers and I've had to put the amps up for sale.
Thanks to everyone for the suggestions, so far. jond I've really liked what I've heard from Audio Note speakers at shows. I simply wasn't aware they were efficient enough to pair with the Frankensteins. 

Are the J's their entry level model, and the E's the next step up? It's very difficult to understand their line, with so many versions of each model, and no price lists that I could find to differentiate them.