Given the number of Democratic contenders in each debate (usually 9, except when someone's scheduler screws up), and the tiny fraction of time each one spends actually talking (1/9th of the total time) and interacting with the others (2/9ths of the total time, at best), wouldn't it make sense to have debates with smaller numbers of candidates, whether it was 3, 4, or 5?
I'm not sure about the logistics -- candidates could draw straws (to keep it random; it doesn't take much to imagine Kerry, Gephardt, and Lieberman agreeing, "Let's jump Dean!"), the sponsoring organizations could string together 2 or 3 smaller and shorter debates back-to-back (first four, followed by the second five, or 3-3-3), and it might fit better with congressional schedules (though you'd get a lot of Clark-Dean-CMB-Sharpton combos on the road, and a lot of Edwards-Gephardt-Kerry-Kucinich-Lieberman debates in DC).