OK, the PCP-heavy / Springer-light thing, is a general "rule of thumb" that springers prefer lighter pellets, and that with a heavy pellet a PCP will be more efficient than a springer would be.
That's down to the nature of the power delivery.
It doesn't mean you MUST use a heavy pellet in a PCP
Your results show that the Daystate kaiser,
as a particular pellet, is not efficient in your barrel, because it gives less power,
it doesn't mean that an H&N/Crossman/RWS/JSB/AA etc pellet of the same weight will not be effective.
Also just because the gauge on the QF goes up to 250bar does not automatically mean that you can fill it to 250bar
the Safe Working Pressure (SWP) of the rifle air tube, is the same as it was before you fitted it.
As to the question of more shots,
you have already doubled the count of consistent shots, if you turn down the reg you will get a few more but at lower fps.
However, if you find a more usual weight of pellet that is efficient in your barrel, that will be a fair bit faster, so will give you a bit of leeway to tinker with pressure.