Im not saying pilots dont wear beards. I know its prohibited by most (if not all) company ops manuals in the US (which are regulatory by nature since it needs FAA approval).
I dont know when you used to fly with a beard, if it was done prior to 1987 (before the study, you mention F-4, but that could be after as well), but it only really takes common sense that you will get a better seal on a smooth face than if you had hair between your face and the mask. No matter how trimmed the beard may be. Unless you're able to get the mask around the beard, such as a short goatee.
As i said, i have never seen any active line pilots in the US with a full beard unless they were piston drivers that dont have a mask on board. There may be many who wear beards abroad. Thats what i was trying to find out. Thanks for the input guys...