I absolutely love my HD250 Linear 1 (600ohm) Made In Germany. Not sure if I lucked out but it is just sublime. That version with more distortion on one side than the other you are referring to:
https://diyaudioheaven.wordpress.com/headphones/measurements/brands-s-se/hd250-linear-ii/
Who knows what was going on with Solderdude's set, but he is pretty picky and even he himself still regarded that particular set highly. On other forums archived on Google such as GrahamSlee, you may come across other measurements.
It is easily one of my favourite headphones just because of the frequency balance. Such an excellent mid-range, and while the bass isn't as detailed as my LCD2 it has a great presence and very good extension. The highs I find almost perfect of all the headphones I've owned. They may look exaggerated on graphs but to me have the right detail and air. I also really like how open the 250 sounds for a closed back.
Just having a session right now my LCD2 early rev and the HD250. While the LCD2 will technically edge out the 250, the 250 has a my preferred frequency balance (with perhaps a bit too much bass).
I'd probably love the HD540, and if I didn't have as many headphones and my LCd2 I'd probably jump on it. My other open back, the HD700 I'd keep because it does something totally different.
The HD250 sound authentic - they are the epitome of what a reference studio closed-back professional headphone should be.