I can't relate to level-per-session averages. I have to ask for hours-per-level averages because we play a minimum of 10 hours (2pm-12am) and a maximum of 12 hours though usually we end somewhere between 12:30 and 1:30 (except for the first game I DM'd, played til the sun came up

oops! And everyone was still awake, musta done something right).
Normally we level about once a session because our DM's have this problem with presenting "20% of your resources" encounters and prefer 100%-120% 5 hour I-Don't-Know-How-We're-Gonna-Make-It-Outta-This-One combats. Though I'm attempting to slow that in my campaign to about once every four sessions. But as we alternate campaigns every week between two DM's, my game is every two weeks (I voted very strenuously against this as not only do you have two weeks since you did something, but you also have 10-12 hours of some other game stuck in your head to further erase any continuity from your mind, but alas, 5 to 2 isn't even close to a majority)---some people are complaining because they are used to once a session and now it's once every 6 weeks which to them is felt like once every 60-72 hours of play (even though it's half that, another thing I don't like about the system).
That and the body count on the campaign is up to 7 (extremely high for us, especially before 10th level) which is making some of them start new characters and some of them to get raised which either way is costing them levels or in their minds 60-72 hours of work.
So go figure, find something that is fun for your players that won't make you uncomfortable or terminate your game before you are ready for it. And remember, high level gaming is COMPLETELY different (totally different animal, can't stress this enough) than low level gaming but it is just as fun and even more rewarding once you get the hang of it. You get what you pay for, and while high level gaming costs more in every department, the payoffs are stories you can tell to non-gamers and they'll think it came out of a book or an anime.
