If you're a Numerical reader, you know that I enjoy a rather little-used (as in, I'm pretty sure I'm the only one who uses it) stat: points per trip inside the 40. I'm not a big fan of defining only the last 20 yards as the red zone and comparing teams based on their ability to score inside the 20. There's a reason for this: there really isn't a huge range between really good and really bad red zone teams.
Or at least, there's a larger range if you look at the last 40 yards. It better incorporates place-kicking (almost every team should be expected to make a vast majority of its kicks when inside the red zone, even taking into account the general sketchiness of college kickers) and gives us a good read for which teams take advantage of even decent scoring opportunities.