Scoring on Used Thiels here

Was an owner of the CS 1.5, 2.2 and 2.3 but the 2.2 were my all time favorite and listening to piano music from another room sounded unbelievably real; newer drivers were not my cup of tea.

Wig

Thiel appeals to me.  The low efficiency is a concern for me.

The efficiency is about average, actually. Most models rated 87-89 dB. The "problem" is the low impedance. Thiels draw a lot of current. You will want a high quality amp with a decent 4 ohm rating.

Years ago I drove a pair of CS1.6s with an Ayre AX-7e. That amp is rated at "only" 60 W but doubles into a 4 ohm load. That amp had plenty of balls to drive the Thiels as loudly as I wanted.

The amp quality part is very important. Thiels are highly resolving and will reveal weaknesses in your amp, cables, and sources. I'd MUCH rather have a high quality 60 W amp (again, with a 4 ohm rating) than a 200 W meh amp. BTW, a zero-feedback design sounds fantastic with Thiels, IME.

What Thiel models are you considering?

C5i doubles down to 4 ohms according to specs. I don’t see a problem there. It does well with my Dynaudio Contour 1.3mkii monitors which are likely in same class as Thiel in terms of amps needed for best results. SPL is somewhat limited I would say.

I am open to any model though the less obtrusive physically the better.  WAF matters in that room. 

How much bass can the room handle?

Hi,
I caught your post, because I have a possibility to get ones to restore CS 3.5.  This pair will require at least replacement of one woofer and foam surrounds. I've never been in Thiel camp, but more certain than not that I have proper electronics to push. 
Owner will accept trade and I'm planning to trade Technics SL-D3 fully auto turntable only no headshell, dust cover or cartridge in full operational automatic condition. The turntable like that probably has value of $89max, but certainly was picked up by me from estate junk to restore.