Martin Logan Spires or Magnepan 3.7?

Thanks for the reasoned response bombaywalla. I really appreciate it.

Contrary to what was said above, the Maggie does not present a capacitive load to the amp like an ESL. It is essentially a resistive load, very flat impedance curve around 4 Ohms, and thus much less reactive to an amp than an ESL. I have heard both speakers the OP asked about. The Maggie presents a bigger sound stage and more extended highs. The ML has more defined imaging but less expansive sound stage. The ML probably still has little bit better midrange clarity. I prefer the more tight tuneful bass of the Maggie over the more thump of the ML cone driver. The Maggie is more integrated from top to bottom than ML where its cone driver sounds separate from the electrostatic driver. Overall, I prefer the sound of the Maggie with it's livelier presentation. However, the Maggie requires at least 300 watts of good solid state power or 200 watts of good tube power to truly come alive.

Thanks so much Dracule! That is exactly the info I'm looking for. My Jeff Rowland delivers 250 into 8 ohms and 500 WPC into 4 ohm speakers. Should be enough?

This is an old thread but must say one thing the new ML speakers 
integrated seamlessly especially fro Montis ,Summit, and new Impression series 
these are better then stock Maggie with Mye  stand that helps  but 3.6 or up 
much more imposing on the room .