[tdockweiler]

I had both versions and they sounded a little bit different, but this is going off memory.
The first one had very bloated bass. Recessed mids and vocals, especially female felt quite distant. This pair also had a slight lack of treble.
 
I purchased one in 2011 and it had much better mids. The bass was slightly elevated. Just a tiny bit more than my DJ100. I got an impression of much more treble too. I would say overall it was more balanced sounding.
I actually felt it was more balanced sounding than the MDR-7506 I had at the time.
 
BTW one of those graphs looks strangely similar to the Tony Bennett/DJ100 graph. The DJ100 doesn't sound like that graph IMO just before the upper mids, which is a good thing.

 

[CirrusPilot]

The M50s I tried a few months back (not burned in, if you believe in that) had disgustingly bright highs. I listened both unamped off an iPod playing lossless and amped off of my vinyl rig, and in both cases the mids were practically nonexistent. I didn't find the bass to be too overpowering, but I could not handle the highs.

Maybe the pair I picked up were bad, but I feel like the M50s have a very deep V sound signature