To characterize the difference between the .7 and 1.7 I would have to first mention the increased size of the drivers themselves - you get a much larger radiating surface with the 1.7's, ergo, a "fuller" sound. To my ears the increased mid/low range response seemed to soften the highs somewhat, and I felt the soundstage/overall sonics were more detailed from the .7's. Again, a highly subjective impression but one from an individual who truly loves Maggies.
Until I came across Thiel, Maggies were my reference point for loudspeakers in terms of sonics. The first time I played the MMG's I was quite literally astounded. $599 for a pair of speakers that sounded like THAT? I was patting myself on the back for a good amount of time after that. On vocals and jazz they were/are truly exceptional, eclipsing my current Thiels in some respect. (CS 3.6)
Both of these brands have an undeserved reputation for being "power hungry" loads on amplifiers, but in my case it's been decades since I've listened to Led Zeppelin I at a level that would make my liver and other internal organs quiver. On the other hand, Thiel, like Maggies, "reveal" - they are as revealing of good electronics as they are to lesser ones, an aspect which often finds one on a quest to find amps/preamps to make them sound their best.
Again, I suggested a REL sub to complement the .7's because I found the bass panel, and its connections, to be less than desirable sonically and esthetically. I used a small 8" REL in my 14X24 room with a ceiling that slopes from 8 feet to 17 feet at the apex. My listening level is VERY conservative, and that setup fit the bill for a while. However, becoming a member here a little while ago has inflicted me with a serious case of audiostupidiosity, an incurable malady many of us share, even revel in.
I bought my MMG's new, direct from Magnepan. I bought a pair of MGIIIa's used from a gent 80 miles away, and my pair of .7's used from another gent in NYC, about 60 miles away. In my experience I find that peeps who own "good" stuff tend to care for it during ownership and I've yet to encounter an instance buying on Audiogon which could challenge that.
In all the instances I picked them up personally. I'd have some reservation about having a Maggie shipped for obvious reasons.
I believe the OP can find a very happy space with the addition of a good sub at a nominal increase in outlay. The MMG's are remarkably fine loudspeakers to begin with!