Ran it on HPA for a time (1200 and them 850psi). Decided the only real good reason to have a .25 is for power and larger critters in mind (if less power would do the trick, would use a .22)...so put that .25 upper on a PCP tube and run it to +50 foot pounds.
(honestly, its my least used airgun...just not a whole lot I shoot that needs to be hit that hard)
Think you can get the power of a .25 up with HPA (esp. 1200psi). The odd thing is that I was moving so much lower pressure HPA air to get it up to +40 foot pounds that it is noticeably quieter running as a +50 foot pound PCP. The little blast of 3K air makes less noise (or rather allows the LDC to better handle the volume) than the big long blast of 1200psi air.