Overcast can't beat afternoon light. It just doesn't have the same modeling qualities. There's one exception: right before an electrical storm. All sorts of magical things happen then. A couple of your shots above are made with light that veers in that direction.
As to which film/developer for overcast weather: I use routinely Trix at nominal speed with D76. It doesn't get more basic than that. ISO 400 films are practically designed with overcast weather in mind and they give proper contrast with viable shutter speeds for moving subjects. If we are talking UK-in-January kind of overcast then I push one stop. Heck, maybe even two. In which case HP5+ also looks really nice.
Nice shots by the way Taylan, nothing boring about them.
.