My point regarding cost of the unit is that you won't be buying either a unit of elites or a unit of heavies.
Also on the subject of defence die: The white die is marginally better against elite stormies or royal guards, against weaker things black is a lot better (16% or so against regular stormies), against stronger things white is better. So given what I understand of the meta a white die is in general better.
Edited by Norgrath