Im making performance tune on my markers self (one reason is that it cost to much money send the markers from Europe to USA and back).
With untunned old style PGP you can get only 8-10 shoots above 240 fps. I have seen velocity graphs from PPS tuned PGPs which can get 50+ shoots above 250 fps per powerlet. I have a little doubts about that, but surely it is possible to get 40+ shoots... but you really need entlarge the hole and respring
the marker. The valve body makes itself only very small difference without this.
Here is velocity graph from PGP with standart (4mm ID) hole and the same marker with entlarged 5.2mm ID hole (resoldered
tubes and discharged .22 LR carridge was used like new tube). You can see that even without all other mods there is big difference:
With ligtened hammer and different springs I can get 17-22 shoots above 250 fps from such like marker. And I mus say that the 5,2mm hole is still smaller than is will be optimal (Optimally the hole between tubes has the same or even larger diameter like the central hole in the valve... the stock valve has 6.8mm ID). When you resolder the marker, you can use .32 Browning carridge what will make 6.85mm ID hole. The results are then even better.
Because there are many spring combinations usable for every valve/hole/hammer weight combination, but only few are the best, you can spend many paint and time to find them. So perhaps it will be wise send your marker to Palmer. He is the best expert for PGPs. The question is not if he can
make the best for you PGP.