ΔE 16.6, loose: different enough that you should pick on purpose. Titan Buff is noticeably lighter, more saturated than Great Hall Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Titan Buff is noticeably lighter, more saturated than Great Hall Grey.
The same difference applies the other way round: Great Hall Grey is noticeably darker, 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.
See Great Hall Grey on the colour wheel See Titan Buff on the colour wheel
All matches: Great Hall Grey equivalents · Titan Buff equivalents