Kricket Questions (25 cal)

For those of you who have the standard size, 25 cal, Kricket, I have the following question:
To get the JSB Exact King Heavy 33.9 grain pellet up to 900-925 FPS, what psi do you have your reg set at and did you have to get a different hammer spring? If so what and where did you get it? Also what is your shot count before it falls off the reg?

Thanks in advance.