Your college doesn't generally matter to potential employers. Your degree is conferred on you by the University, not any individual college (or PPH), so there shouldn't be any difference in perception (you don't need to put your college on your CV). If anything, for theology degrees it might be preferable to study at a PPH, although I can't speak with any sort of authority on that; otherwise there's no difference as far as I know.
PPHs are essentially the same thing as colleges, at least as far as students are concerned. The environment is obviously a bit different, considering that they're much smaller than colleges and also they tend to offer only a very limited range of subjects. But if you think you'd like to live in what is probably a more 'cosy' environment, then PPHs are certainly an option. There's no difference in reputation.
Don't know about Cambridge, sorry.