Insulation – Roxul versus Fiberglass – GreenBuildingAdvisor

We are building in zone 3B with a conditioned attic.

Does Roxul ComfortBatt R38 insulation at the roof deck and R21 in the exterior walls perform better than fiberglass insulation of the same R value?

It is about $20k more to use the Roxul Comforbatt insulation and I am having a hard time justifying the very high cost.

Would be interested to hear thoughts of people who have gone one way or the other.