Quietest ever? I'm not sure which it would be, but I know for certain it is not the P-22 or any semi-auto with or without a slide lock. The longer the barrel, the less heat and noise that reaches the muzzle.
A break open single shot is not as nice as a semi-auto, but it can be much less noisy. Add on the oversized silencer and it makes a difficult combo to beat in the noise or accuracy department.
If you really need a repeater, then this old beat up 1895 Nagant will probably best the P-22 in the accuracy department any day. The target loads move a 93 grain bullet at about 700 fps, about the same power as a 22lr. Full power loads are still subsonic but a bit louder.
Ranb