The PMR isn't the most gas efficient marker out there, to get the most out of it a 4,500 psi 1.1 litre system would be best (this being the pressure you can fill the bottle to abd the empty volume) as for output pressure, IIRC the manual says 400-800 psi, so either a high or low pressure system would be fine. Some systems are a mid output like the Dye Throttle.
If you save money by buying a 3000 psi system it will probably be a false economy as the next thing you buy will be another air system. Even if you change the gun you can keep the air system.
Hope that helps.