I just compared headphones that I am interested in.
Looking at frequency response graphs I can say that LCD2 must sound really brilliant, while HD600 would be lacking bass. The Momentum's and HD800 have very similar graph up until 2kHz. I would even say that Momentum's graph is even closer to 0dB flat line, than HD800's which is more of an arc than a flat line. After 2kHz Momentum's go rapidly down with -15dB dip at 4.5kHz, and then climb to -10dB at 10kHz to go down again to -30dB at 20kHz. The HD800 does opposite: there is a hill 7.5dB over 0dB flat line between 5kHz and 10kHz, which must sound little bit disturbing. If you look at LCD2 it has very nice almost linear response from 10Hz up till 1kHz and then it gently goes down, with some hill at 7kHz, but it's still 3dB under 0dB flat line.
These look the same for all thee compared headphones.
Here we can see LCD2's constant impedance regardless of frequency. I assume that makes them easier to drive more accurately.
50Hz Square Wave
LCD2's version way more resembles square, while for others it's more trapezoid than square.
500Hz Square Wave
On this graph surprisingly Momentum's are closer to LCD2's than HD800, and compared to them the HD600 came vary bad.
Momentum's cost 1/6 of the HD800's price, but it's possible sometimes they'd sound better. The HD600 (at least from graphs) look very disappointing. The LCD2 is something that astonishes me. Their graphs tell me that they are worth their higher price, so I think next step after Momentum is LCD2:)
This entire thing and its conclusion is complete garbage for an almost uncountable amount of reasons, but there are two huge ones that are easy to point out. First, graphs mean absolutely nothing in that they don't tell you how your ears and brain interpret sound which is also highly subjective. Second, and the much larger one, you're making conclusions based on headphones you have not even listened to.