Audio Research Ref 150 or 250 with Maggie

Bifwynne is right. Ask Kal at ARC. ARC has Maggies (as well as Wilsons and Sonus Fabers) in house. He will not lie to you.

If you can afford the Ref 250 mono blocks and have the space for them that's what I'd recommend. I think the mono blocks would most likely sound better (by a slim margin) then the 150 but it's a matter of dimensioning returns and only you know your financial situation. I believe the Ref 150 would work nicely. I'm not sure if the Ref 75 really has the power you are looking for to drive the Maggies? As was mentioned Kal at ARC would most likely know.
Please post your findings here, because it's a really good question that has come up before but no one seems to post their findings.
I drive my 3.7's with a Plinius Reference SS amp so I think I have 450 watts per channel.

Don't know if this will help in your decision, but I have both a Sanders Sound Systems Magtech amp, which is SS, and a pair of VTL MB-250 Signature monos. I use the VTLs in the cooler months only because my room is above the garage and gets too warm in the summer. Speakers are Maggie 1.7s and I prefer the sound with the VTLs slightly over the Magtech because it has more dimensionality. A somewhat more spacious sound. The difference in power output between these amps is substantial, 900 for the Magtech into 4 ohms vs. 250 tube watts for the VTLs. The room is not a perfect rectangle but the approximate size is 19 x 15 with an 8 foot ceiling. BTW I just had to spend $4400 for a new furnace so something has to go and I've decided it's the VTLs since I can't use them all year long. Let me know if you are interested.

The Ref 150 should work fine. I used a ARC D125 (115 w/c and had more than enough power on MG IIIa speakers. I am no a headbanger so YMMV!

I have the 20.7's, had the 3.6's previously. IMO you will be disappointed with the AR 150's, not enough power. The 250's will do the job, but are a very pricey option. I have tried many amps with my Maggies and the best by a wide margin are the tube amps that I use now; the Carver Black Beauty 305's. The Black Beauty's use six KT-120's per side and seem effortless at driving the 20.7's. I never feel that I am lacking power or dynamics no matter how loudly I play music, rock or large scale classical. My room is failry large too, 17.5 x 26 x 9. The Black Beauty's make the 20's fill the room with sound. They will not be quite as extended on top as the AR but they will be more 'organic' with richer tone. You can tweak that a bit by changing the 12AX7 input tube on the amps, adjusting bias, and by using the built-in feedback swtich. Check out these two reviews and this video review on Utube:

http://www.theabsolutesound.com/articles/carver-black-beauty-305-power-amplifier/

http://www.enjoythemusic.com/superioraudio/equipment/0512/bob_carver_cherry_180_tube_monoblock_amplifier.htm

http://m.youtube.com/watch?v=uBBlDNCW0UE