My understanding is that scuba tanks are pressurized to about 6,000 psi.

I wouldn't use 2000 psi or anything near 6000 psi air pressure on a pneumatic cylinder without confirming that the cylinder and all the hoses carrying that air are rated for that kind of pressure.

If you put 2000 psi into a cylinder rated at 300 psi, you've got a pipe bomb.

Since most air compressors operate at about 120 to 150 psi, I expect that'll be what most pneumatic equipment is rated for. Maybe 300 psi to provide some safety factor.

But, I doubt you'll be able to find a pneumatic cylinder rated for 2000 psi. I don;t know what would happen if you put 2000 psi air into a hydraulic cylinder rated for 5000 psi oil pressure, but at least the cylinder wouldn;t turn into a pipe bomb.