Thats the trouble with guessing by ear.
But its not bad for an initial setting.
JSB 25.4 = 870fps
Kodiak 30.6 = 810fps
Also guessed wrong about the sweet spot pressure; it is lower than guessed. Rather than 2700psi, its more like a 2400psi sweet spot. So there is room to move up in fill pressure and readjust the gun to run right.
Won't be a lot of shots. That tube has a volume of something like 106cc's. Running an air efficiency calculator a few times, even if I got it tuned to very low air use, will be a short shot string at that energy level.