And I have been very selective through the many years of detecting and headphone options that come along.
Let me add one more model for your consideration then I'll answer your question.
You have the Grey Ghost Original, and they are very good headphones. You asked about the Grey Ghost Ultimate. You also asked about the Killer B 'Wasp' and those used to be the headphones I favored. Now let me add one more consideration, the Killer B 'Hornet.'
First, your headphones and the other three models listed all use 150 Ohm impedance speakers, which I like.
Second, the Grey Ghost, Grey Ghost Ultimate and Killer B 'Wasp' all use, if I am not mistaken, the same/similar size, shape and style hear cup. I found those to become uncomfortable after a longer period of detecting, and also let in too much wind noise when I was searching a windy beach or other location and had to deal with high winds or nearby traffic noise
I made the switch to the Killer B 'Hornet' because they provided me the same speaker type and adjustments as the 'Wasp,' but they are in the 'tank' style ear cups. Those don't press on my ears uncomfortably, but cover the ear. That is not just comfortable but it blocks out wind and other outside disturbances.
Third, the Grey Ghost design utilizes a single Volume Control knob to adjust for both ears. I am deaf, according to the military and those who get annoyed when I keep asking "What?", and to add to my aging deafness I fell off a ladder seven years ago yesterday and ruptured my right ear drum. It healed, in time, but with scar tissue on the ear canal and ear drum so that makes listening an even greater chore. It also means my hearing in each ear is different, and there are a lot of people like that, so it is better, for me and many others, to have separate Volume Controls on each ear cup to adjust for each ear.
Both the Killer B 'Wasp' and killer B 'Hornet' models have separate ear cup controls. So, my personal pick would be the Killer B's, especially the "Hornet' style. I'm trying to trade an as new detector and get a couple of sets of 'Hornet' headphones as a partial trade. That way I can keep one set in each vehicle and one in my back-up accessory tote.
Monte