sml19, sorry but no experience with the .7 for a direct answer to your question.
I have a pair of 1.6s modified by Peter Gunn. Unfortunately he passed away and his Magnestand site is no longer up. He had reasons he did not recommend the 1.7s. Also he didn't modify any larger model than the 1.6. But he was controversial and many on the Planar Asylum disagreed with him.
I have heard the MG 20.1 and thought they were exceptional.
I think contacting Magnepan will receive a recommendation for one or another of their new models. Big surprise. So the best answer (as always) would be to somehow audition one model or more in the current lineup.