ΔE 6.5, close: similar, with a visible difference side by side. Nurgling Green is a little lighter, cooler than Yellow Green FS-34259.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Nurgling Green is a little lighter, cooler than Yellow Green FS-34259.
The same difference applies the other way round: Yellow Green FS-34259 is a little darker, warmer.
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 Yellow Green FS-34259 on the colour wheel See Nurgling Green on the colour wheel
All matches: Yellow Green FS-34259 equivalents · Nurgling Green equivalents