I can't reference any studies or anything, but my personal experience is that passion trumps all. The problem with passion is, you don't have much of a choice. One might have a passion for gardening, whereas another might have a passion for computers. The gardener has a lower chance of being "successful" and "making a difference" (in the standard capitalist/western sense).
Many studies have found that IQ predicts financial success regardless of childhood socioeconomic background or profession. Running a chain of greenhouses lack the flashiness of, say, particle physics, but it can be both profitable and socially important.
