The LCD3's soundstage really opens up with a lengthy burn-in. I'm not talking 120hrs here, no, more like 500-700hrs. I'm currently at about 700 hrs and I'm no longer burning them in. The soundstage is much wider and deeper now for me than when they only had 200-300 hrs. I'm using the DHC Molecule cable and I think it too takes a considerable amount of burn-in before it sounds its best. This is my third DHC Molecule cable and for each one I noticed that they became much better after about 450 hrs. Soundstage is only one of the improvements I heard after burning in the LCD3. Its bass became much tighter, deeper and more defined. With the DHC cable, the bass was a bit to prominent until about 400+ hrs and then it tightened up considerably. Highs became a bit less bright while becoming more delicate and defined.
I kept track of my burn-in hours so I'm sure of the hours that I stated above. The only variable that may be different for you is that I used the DHC cable. However, I have cables from ALO (HD800 and LCD2/3), Moon Audio (HD800), Norse Audio (LCD2/3) and Jenna Labs and all them took about 400+ hours to sound their best. At 100-200 hrs I felt that the LCD3 should have been called rev3 because it wasn't offering a huge improvement for double the cost. Now after burn-in, the LCD3 is a big step up from rev 1 & 2 and deserving of its much higher price tag (IMO of course). BTW, I still own the rev 1&2 so its not just from memory that I state the LCD3 is a big improvement over them.
My intention is not to turn this discussion into a debate on burn-in but to relay my experience. If you don't believe in burn-in or you think the amount of hours I burned them in is ridiculus, so be it. I'm not going to debate what I hear. I used a separate burn-in setup playing the same CD 24/7. I think a common mistake regarding burn-in is that people will check the sound too often (like every 24 hrs) and not hear any change and then mistakenly conclude that the burn-in is complete or burn-in is not effective. My recommendation is to burn them in when they are not on your head and don't expect daily changes. I've also heard a roller coaster effect where the SQ actually got worse before it got better.