There is a
new tool on the website that allows people to analyze load factors, payload etc over time for routes, airports and airlines.
Anyway some of it is helpful for commuters, as it helps identify load factors by airline, route, and year. I printed out a couple that might be helpful for the LAXPHX commute.
LAXPHX on SouthWest
LAXPHX on Delta
The link up top is linked to a page with a bunch of Virgin America Statistics.
Obviously, talking to someone who actually runs the commute is the best, but hopefully these two reports offer a little insight.