New Mag 3.7i vs Sonus Faber/Wilson/Mcint 2nd hand?

I have heard some of these in different systems. 
I have heard the Sofia 3 on a number of different amps. 
The Sonus faber on Classe

The Maggie’s on a mc352 or mc452. Not sure. 
Anyway these all sound really different. The Sophia 3 is a great speaker with great bass with good solid but not amazing mids. The highs are showing their age though. Still fine but not on pair with Focal and Revels’ newest offering. The highs while fine show some hash and lack of air compared to the best these days. I think the highs are fine though. I feel like tue drivers lack some integration and setup is hyper critical to get everything to blend right. Millimeters matter. I like this speaker better than the Sabrina. Though I might take the Sabrina with subs over the Sophia without. 

I think you need an Olympica III not two to hang with the Sophia. The Olympica is comparable to the Sophia. I feel like the Olympica III has a rounder mid bass and is less dynamic in the bass. Mids are comparable in quality but have a different tone. The highs are better to me than the Sophia 3. Very nice speaker. 
The Maggie’s are a different animal. They have amazing highs and are pretty good in the mids. They lack dynamic impact in the bass for me. Since I listen to a lot of modern music I have always passed on them. They make Norah Jones sound magical but make Metallica sound dull IMO. I feel like they need to be played at ear bleeding level to have the pace I want for modern bass heavy music. The sweet spot is small but the sound is huge once in it. 
Of these three speakers if I were to get a pair free I would take the Sophia 3 as I put a lot of value on the bass and dynamic impact. The Olympica is not far behind and with better highs and mid range integration if you listen to more tame music these are a very good buy imo and a steel at their current used prices. 
Maggie’s are cool but a pass for me. Make sure you demo before you buy. Try all types of music. 
I would add a new/used pair of Revel 228be/328be to your list. I feel these are the best speaker in this new/used price range. Amazing highs, detailed and airy without being fake or harsh. Good mids, great bass impact and not picky about setup. 

Thanks for your great input. I plan to run them along my two SVS SB4000 subs which cover the base end.

You have to decide if you like flat panels or not. The Maggies can do wonderful things if you can put them where they need to be placed and have the power to drive them. 

Running subs opens your options (I also run duel subs). The bass is really where the Sophia shines over the others. But with the subs the others might pull ahead. Especially if you highpass. If you are not high passing your subs I bet that would improve your system as much as new speakers. Something like the JL CR-1. 

There are used Sabrinas for around 10k too. They would be very comparable to the Olympica line. I have demoed them too. The Sabrina is probably just a hair harsher in relative terms in the upper mids than the Olympica (from memory in different systems so huge grain of salt here…) and the Sabrina has a little more bass impact. Highs are comparable.