I sent my LCD3 to Audeze for the fazor upgrade.
The result was unbelievable.
The headphones sounded much transparent, the highs sparkled, and I could differentiate sounds I never noticed before.
I never heard the LCD X, but I can tell you for sure that the fazor upgrade will make your LCD3 a completely new headphone.
The fazored 3s are indeed more airey and detailed but do you find that there isn't as much punch and rumble in the lows as the classic?