It strikes me that logic and forethought might be particularly Slytherin virtues. Slytherins are also pragmatists, in that they want to get things done and generally (Regulus, Severus, perhaps even TomRiddle) succeed. They also have a great capacity for personal love and loyalty. And I think patience might be more a Slytherin virtue than a Gryffindor one. Given that they are the water sign, they should also be flexible (but we don't really see that in canon) and deeply emotional (that we do see).
Just my two cents.
Just my two cents.