I use NPH or Ultra 400 if I want a 400 speed film, but as Mick says 800 film works well when exposed at 400 and it gives you the option of exposing it at 800 when you need it. Even exposed at 800 the graininess of Portra 800 should be unnoticeable if you are enlarging the short side of the neg to 12" (depending on technique, of course). I put Portra 800 through carry-on film scanners at US and European airports quite frequently and have had no problems.

Best,
Helen