The .25's do deliver a power boost over the .22's for sure.
Some FX's do fine with bullets, some don't due to being rifled for diabolo shaped pellets.
N.O.E. Bullet moulds in Oregon (I think) has a special run of 22 and larger bullet moulds for air rifles, called Bob's Boattails.
I have one of these moulds for my Condor, casting 4, 51gr. FN BT's per throw. The moulds are beautifully made, aluminum & and finely finished. He also makes HP designs as well as a varity of hollow based weights in different calibers.
The hollow point cavities are adjustable on some moulds.