The Pentax P cameras are interesting because they have AE lock, one of the very few Pentax cameras w/ that. So they're good in that respect. But the shutters are pretty loud, more of a "thunk".
If you shoot an AE camera w/ AE Lock, you can get an accurately metered shot off quite a bit faster. I set my aperture where I want it, let the camera choose the shutter speed (you can do this the other way around too of course), and lock the exposure w/ my thumb. A motorized film advance is advantageous too. I know you mentioned you weren't looking for Canon glass, but the Canon FD lenses are terrific, very good image quality, especially the 50 1.4 and 85 1.8 lenses.