Any reduction in back pressure promotes good suction at the injector. Most guns rated at 8 to 10 gpm offer little restriction, so there should be no problem as long as the gun is in good shape. As the actuator rod wears, trigger travel will reduce, altering the clearance of the ball off the seat.
I have seen balls of varying sizes for sale but a larger ball won't really help, I don't think. Regardless of the ball diameter, the hole in the seat remains the same. So, geometrically speaking, lifting a sphere of a different size off the hole would probably not change total opening area much, if at all. Besides, the bore in the valve section of the gun remains the same. How much can you gain, without closing off the diameter of the bore with a larger obstruction. More lift would actually help a little more, I believe. The ideal gun would have zero free play before engagement, allowing more trigger travel.
Now the larger capacity guns (20 - 25 GPM) have much larger passages overall, the inlet pipe, the guts and valving in the gun, and a larger outlet pipe.