Which is going to give higher impact strength?

I am assuming that you are talking about the Nodule Count In Ductile Cast Irons and its effect on the Impact Strength.

As Vishal Pambhar has mentioned rightly the impact strength (Toughness) depends on the Count & Temperature.

As a thumb-rule, you can remember 2 things

1. At very low temperatures (mainly sub-zero), the Impact Strength increases with increase in the Nodule Count
2. At Operating Temperatures, the Impact strength first increases with an increase in the count reaches a maximum and thereafter the Impact strength decreases with the increase in the Count

You can learn more details about this Concept in our coaching classes