ΔE 60.5, loose: different enough that you should pick on purpose. Gold 79 is noticeably darker, much more saturated than Mithril.
Can I use Gold 79 instead of Mithril?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 60). Gold 79 is noticeably darker, much more saturated than Mithril.
Can I use Mithril instead of Gold 79?
The same difference applies the other way round: Mithril is noticeably lighter, much more muted.
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.