Not sure that it totally has to do with head size.
What I think the issue with DC headsets is, is they have a limited amount of adjustment areas.
I've always been a fan of Telex for the size and tension adjustments they have. Never heard of anyone who said they didn't fit right, or wear well after a long flight.
I like the Peltor ANR design as well. Battery in the headset, cord can be unplugged and replaced, Not extra box. And they are fairly comfortable.
I have a set of DCs that were given to me. Nice headset, but I can't wear it for more than an hour without discomfort. My head is about 7 1/2 as well, so not sure it is just a head size thing. Think it also has to do with the angle of the ear seals, and how the DC doesn't allow you to adjust the tension. Maybe undercut earseals are a solution, but I'd rather have a headset fit me the first time.
BTW, a great source for headsets is ebay, so start shopping now. I picked up a couple of Telex 3100s, their basic model, which goes around $200 new. Both of them, shipped to me, was like $41 I think.
For ANR stuff, see if there are any deals out there for instructors to buy them, and have your CFI get the discounted price for ya.