ΔE 16.7, loose: different enough that you should pick on purpose. Runic Gold is noticeably darker than Auric Armour Gold.
Can I use Runic Gold instead of Auric Armour Gold?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Runic Gold is noticeably darker than Auric Armour Gold.
Can I use Auric Armour Gold instead of Runic Gold?
The same difference applies the other way round: Auric Armour Gold is noticeably 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.