Im at lvl 367 and pass than mark by a 1k or more in each field to get a boost from them but that is because I have been lvling up my player and getting armor whenever. So if you got the super sexy armor it might be faster but its going to be better if your have your class stat at legendary maybe. Also you can buy 30 skill point in each field every level. So I would guess you would take your current skill lvl in whatever field you want the boost in the most minus that from 20,416 and divide that by 30÷30¯\\_(ツ)_/¯ cause math.