I executed a comparison very much like you seek several years ago. In my Focal Utopia review, I included a table describing the characteristics of the Sennheiser HD 600 (around $300 to $400), Focal Elex (then $700, now <$500), Focal Clear (then $1,500 now around $800), and the Focal Utopia ($4K+). I included the closed Dan Clark AEON Flow because I had it.
You do get more technical performance at each price tier, but @Nuance is correct. After $300 it’s mostly playing in the margins. Still, if forced to choose I’d go with the Clear over the HD 600 any day of the week. The HD 600 is too vulnerable to scratchy treble artifacts on many amps, while the Clear is cleaner and more forgiving.
I’ve demoed the Utopia a dozen times and very much want to tolerate its treble, but I cannot. I’ve demoed the $6K Susvara, but find it as bland and boring as white bread with a topping of mashed potatoes. No salt. To this point I’ve stayed with my HD 800 S, as a technical step above the Clear and below the Utopia – both in price and performance.