One stop under, at least. If your meter wasn't set to +1 or +1.5 compensation due to metering off pale skin then that would be your cause. And if you were shooting in tungsten light, there's at least one more stop gone (Edit: that looks like window light, so ignore this).
The backlit one is just the meter being confused by lighting situation. You should spot-meter the face in this situation.
If you meter carefully, Portra easily achieves box speed. What you've done here is demonstrate that Portra produces passable-but-not-great results at about EI1200.
Edit 2: the white lines are probably scratches. The overall yellowed look is probably because the scan operator has a poor sense of colour; the film itself doesn't look that bad unless the lab's chemistry is bad. While some labs try to cut corners on chemistry capacity, poor scanning is more likely than poor processing.
The grain is definitely worse than it needs to be, but you aren't going to do a huge amount better on 35mm at ISO400 unless you get (and learn to use; it's a long learning curve) a good 4000dpi dedicated film (not flatbed) scanner or if you print optically. Optical printing requires a bunch of annoying equipment (a darkroom!) but will give you great quality with a very short learning curve, mostly because it doesn't really give you any control Colour printing at home is also staggeringly cheap (excluding your labour costs) compared to any other output process; think 50c per 8x10.
Last edited by polyglot; 02-25-2013 at 11:33 PM. Click to view previous post history.