Giving "career boost" it's usual interpretation, the correct answer is Webb's 3:53 HS mile on Nike's hallowed turf.
Since he never did anything significant in world competition, his decade-plus of compensation at $250K or so per annum was mostly based on being the guy who broke Ryun's record. And did it at Hayward.
Whatever he invested in to achieve the drop from 4:00 to 3:53 in spring '01 was well worth it.