Polished Silver vs Gold 79

How close are they?

ΔE 54.2, loose: different enough that you should pick on purpose. Gold 79 is noticeably darker, much more saturated than Polished Silver.

Can I use Gold 79 instead of Polished Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 54). Gold 79 is noticeably darker, much more saturated than Polished Silver.

Can I use Polished Silver instead of Gold 79?

The same difference applies the other way round: Polished Silver 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.