One other factor I have noted, which points to more velocity is better. When I ho after the rats st night, it's in our chicken coop, shooting is at about 7 yards. The little buggers often hear s noise, from the gun, which are them jump in random direction. The more velocity, the better the chance of nailing the rat before he jumps and makes me miss the shot
It could be that, bearing this in mind, my slowpokey 500 fps Hatsan Alpha .177 break barrel Springer is too slow and too loud for the job. My Daisy 880 is a bit faster with 8 pumps, and fairly quiet too.