ΔE 10.7, fair: the same colour family, but not a straight swap. Iron Fist is a little darker than Ironbreaker.
Can I use Iron Fist instead of Ironbreaker?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Iron Fist is a little darker than Ironbreaker.
Can I use Ironbreaker instead of Iron Fist?
The same difference applies the other way round: Ironbreaker is a little lighter.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.