Important to remember that you IAS during a slip is not a direct representation of the relative wind, the static port is either seeing more or less pressure than normal due to being exposed on the side of the fuselage, depending on which way you are slipping. So 70kts isn't really 70kts. Also, slipping at x pitch attitude (high drag situation), if you come out of that slip and don't change pitch attitude, you're going to pick up a ton of speed real fast due the lower drag, so you usually pitch up some as you come out of the slip, which all means you have to take into account the actual approach path, which isn't quite as simple as aim where you want to go, you have to make compensations.