In my experience, a one stop underexposure needs no push processing on any negative film I've ever used. Tri-X 400 @800, Gold 200 @400, etc. Once you get to 2 stops it benefits from pushing (except Portra 400, which I shot once at 1600 and pushed it a mere 1/2 stop in C41 ... I'm sure I didn't even need to do that).