Differences among the electrostatics of Martin Logan models?

I recently heard a pair of Martin Logan ESL13's (Expression), and loved them, but they are way out of my budget.  I understand the electrostatic portion of the ESL 9 is nearly identical, and that got me thinking about pairing one of the many models of used MLs (eg ESL X, EM-ESL, Ascent, Sequel, Scenario, EFX, etc) with a good subwoofer.  Does anyone know which models of ML use the same electrostatic section as the 9's and 13's?  Which older models would have noticeably inferior electrostatics, and which should just be avoided? 
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I am looking into ML 11’s. The dealer near me didn’t have a pair on hand, so he suggested the ESL X, from the Electromotion series. I was not impressed. The one aspect that bothered me the most was the disjointed  nature of the upper range with the bass. Two weeks later, the 11’s were set up in his shop. Although their placement was not optimized, the sound from the 11’s was totally different from the ESL X’s. The sound was of one piece, bass + upper range, probably similar to the 13’s that you heard.

I believe it is a mistake to go the ESL X route, not I in the same league as the Masterpiece series. I don’t know about the Summit or other similar range past models. If price is the issue, perhaps you should consider the 9’s. After much research, I have moved my gaze from the 11’s to the 9’s.

Thanks ledoux, I agree with you; the X is not as good as the 9; unfortunately, the 9 is out of my budget too, so I'll have to save up for now.  Good luck finding your ESL 9's!
If you can get them with good panels, the Monolith III was a great speaker. I have the latest panels in mine and they can't be touched for sound quality.
I always said if I didn't have these a used pair of Summits would be on my list for a more manageable (waf) speaker..

Cheers George
Figure the cost differently....mine are 8 years old...bought them used.....Figure they last you 12 years....divide the price you are looking at by 12 and that is your cost per year....about the same as a new iPhone....
@palmharbor -- Thanks for your response, I think that's a good way to approach it.  Unfortunately, I listened to several pairs of used ML's, and none of them sounded as good as new ones.  I even listened to a pair of Sequel II's that the owner said had new panels installed 6 years earlier, and they did not sound good.  After trying to find a used pair that sounded as good as the ones I initially heard, I eventually bought a more traditional set of speakers.
You might want to check out Sanders ESLs. He designed the curved panel for ML, left and created his own company. He is an up front guy.
His speakers are significantly better than any ML I have heard. You can not take a curved panel very low before they become completely non linear. Read Sanders white papers they will give you a lot of insight into his thinking and the world of ESLs. 
When comparing different  or even the same ML ESLs, you need to consider the room placement and the partnering electronics. The model you heard in someone else's home/room will sound different in your room. Probably true for all speakers.....
@mijostyn -- thanks for the tip, but $17,000?  I'm sure they sound great, but that's even more than the ML 13's were; I was looking for something in the range of $2-3K.  I will, however, read Sanders' papers, and continue to dream...