That is tough decision especially if you haven't heard either headphone before. Of course, you're gonna then have to consider which amp to drive them with. Although their frequency balance is similar, they're sound signatures are entirely different. Rich, vibrant planar sound vs. Seductive, smooth, layered sound. I highly recommend you try audition both if you can at a meet to help your decision. LCD-2's do a lot of things well (pinpoint imaging, resolution, detail, gorgeous midrange, bass extension, etc.), I would almost call it a perfect headphone, but I do have a few gripes about them (soundstage, lack of air and space, analytical sounding at times). I do not believe they "blow the 650's of of the water" though, especially not a balanced 650. There are some things about them that they each do really well thus why I own both. Though...if I had to pick one, I'd probably go with LCD-2 if budget allowed just because it's easier to get along with.
I find that to actually be somewhat true. I wouldn't say better, but similar. They both are equally hard to drive IMO, I think the 650 may have been a little fussier having tried them on multiple amps and haven't ever really been satisfied until now that I balanced them.