My friend is rs4680(A, A) and he finds modafinil quite effective for increasing concentration, memory and enthusiasm for work. It didn't seem to be a lot of help for situations of sleep deprivation though which is what the study you refereed to was about. As opposed to the author's description, it did tend to make him somewhat 'high' and 'wired' as well as causing a degree of muscle tension and difficulty in 'coming down' at the end of the day. Also doses of 50-100mg seemed optimal and 200mg was way too much. It is difficult to know if this different response is related to rs4680(A,A) or not.