This is a case where practice trumps math.
Later in the game you will typically see these scenarios,
gTWF vs Imp Crit
No deathward / No fort - gTWF wins via Vorp ex: trash
Deathward / No fort - gTWF wins via Hold Monster ex: Epic
Bosses - gTWF wins via Min II (IC built in!)
heavy fort anything - IC loses
I can't think of many places where IC excels over gTWF.
EDIT:
Basically, anything that can't be vorped or autocritted, you can just use Min II