If you have the 40cm ready to go, I’d say have a game with it and see how you like it.
The Gen 9 has a 33.5cm barrel at a larger diameter than 7.5mm. So the extra length of the barrel at a smaller diameter makes the V/P ratio potentially more favourable. I’m a few 0.1 mm shy of having the correct diameter of a stock air cylinder, but some back of the envelope maths puts your ratio at 1.78, which isn’t too far off a 2.0 ratio.
Stronger springs will help bring you up to a 2.0 ratio. At this point I would ask if the Inner barrel extends past your outer? That would be a good excuse to cut it back, unless you’re graceful enough to not knock the inner on anything.
If you haven’t noticed any drop in performance with the 40cm barrel, call it a win and leave her as is. The more moving parts you’re worrying about the more you’re worrying in general. Hard to enjoy a game if I think I’m at a disadvantage thanks to my handiwork or if the blaster is going to break in my hands.