I've always thought that more steps means more rewards. Each step gives one reward, whether its a handful of law runes, a rune full helm, or a robin hood hat. I find that when I do a six step clue I get 6 of these rewards (for example, 2 rune fulls, 34 laws, 37 nats, a magic short bow and a guthix page), and when I do a four step clue I get only four (for example rune: rune plate, rune baxe, 36 bloods and 20 purple sweets). This doesn't mean to say that the rewards for each step is decided after that step is completed, but it is recorded how many steps you've done for the clue when you get your final rewards.