I am in the same boat, I only have 3 "Audiophile Headphones" if you don't include Airpods and various cheap IEMs. I have Sennheiser HD650, Aeon Noire X and Audeze LCD-X, with a ton of different DAC/AMPS, but just like you I have the basis covered, these 3 cans measure so well and provide their own unique experiences, I just don't understand how there could be better objectively, maybe subjectively? how many headphones can a person reasonably wear? after hours of the Noire X at work, I don't go home and listen to headphones, I listen to my Vanatoo monitors with sub.
Putting myself in your shoes, I would be interested in the HD800 (For soundstage) or the Modhouse Tungsten (Out of curiosity) maybe you could try one of the new Hifiman Unveiled products. I am not even convinced any of these are better from a measurements perspective, but maybe they offer something different. That's where I think we are now, its just something different, and for how much money $? yikes! absolutely first world problems here. While I also use PEQ, there is something about new headphones that is not replicable with EQ, I find that EQ can improve the headphones but the sound will always sound like those headphones (If that makes sense) its like ordering a pizza from a pizza joint, changing the toppings and expecting a different pizza experience, it will only get you so far.