Both 1 and 2 I believe decrease the chances of asassination, although I believe spies decrease the chances better(I could be wrong there). Also for balance reasons the spies may work on a bell curve the first one will drastically reduce the chance of asassination while the fifth may make very little difference.

Anyways since the subject is up. Spies can only detect asassins within a certain distance of thier subterfuge from my knowledge, does this seem right to anyone else.