Go with Dulux Palm Night. At ΔE 1.3 from Stable Green it's a very close match — anything under 2.5 is hard to tell apart once it's up and dry, and 1.3 is firmly in that bracket. With an LRV of 4.9 it's a deep, smoky green that does the same job in a room: dramatic, enveloping, and brilliant in a space where you want the walls to recede and the woodwork or art to pop.
The other contender, Dulux Heritage Green, comes in at ΔE 4 with an LRV of 5.8. That's a noticeable step away — you'd see the difference if you held the two side by side, and it reads a touch lighter and greener. It's a perfectly nice colour in its own right, just not the match you're after if you're trying to replicate Stable Green.
Now, the honest caveat: a colour match is never just about the hex value. Paint & Paper Library's Architect Matt has a particular flat, chalky depth to it that Dulux's finish won't perfectly mimic, especially at this end of the LRV scale where sheen and pigment density really show. A close ΔE gets you the right colour; it doesn't get you the exact same texture of light off the wall. If the room matters, that difference can be worth paying P&PL prices for.
My advice: order a sample pot of Palm Night and paint it up against the original — two coats, on a bit of lining paper you can move around the room at different times of day. Deep greens shift hard between daylight and lamplight, and you want to see how it behaves in your space, not in the shop. If you're matching to existing Stable Green walls, even a 1.3 match can show a faint join, so try to break at a corner rather than mid-wall.
For the budget difference, Palm Night is the right call mate — just don't skip the sample.