I bet you're looking forward to April!
Can't speak to what influences beard thickness but regarding length, look at their legs too. A long legged turkey is often a long bearded turkey. Beards on short legged birds are more prone to break off the tips as they feed. Lowcountry SC, coastal GA, and Florida birds are skinny but TALL (maybe an adaptation because of all of the water?). Merrimams on the other hand seem to have way shorter legs (and beards) but it can be rocky out there too which break off beards (vs sand).
Hope you get a crack at'em.