The link below leads to the reputation guide which does a pretty good job of explaining how reps are rewarded, not only is it the number of attacks, but different attacks have different rewards. Since the max possible reps is usually the goal, and reps are rewarded based on a. attacks used, b. number of times each attack is used, and c. survival, one must weigh in a few alternatives to determine what combination will yield the most, and it will vary from enemy to enemy, weapon to weapon, level to level.
http://www.piratesonlineforums.com/f...ead.php?t=6926
An example, regarding one thing you mentioned. Using Take Aim with pistol will reward more reps, but it does more damage, so you get in fewer attacks.
Higher rewards, fewer attacks (hint release it the second the power bar shows up to do least possible damage, and increase number of attacks).