Because the 3.7 and 2.7 are the same size (24x71) I'd go with the 3.7x. I have had all 3 of the Maggies in this topic and BY FAR the 3.7x is the king. (insert approved audiophile superlatives here).
There is a "secret" that the Maggie insiders don't talk about. Sometimes Dave Gordon lets it slip out: The 2.7 is a flawed design. It's the tweeter. That's the substantial sonic difference between the 2.7 and the 3.7.
I was not happy about the $4000 price increase for the X. However, after owning a pair- and doing side by side listening to 3.7 v. 3,7x I can tell you that the cost is fully justified.
Of course this is just 1 (experienced) man's opinion. Go listen for yourself. You will be surprised.