I think recipes call for overripe bananas because they devolve into a smooth mush without much trouble. The recipe I use, from the superbly creative Alton Brown, calls for using a potato masher to mash the bananas. Even firmer bananas mash down into a decently liquid pulp. Yes, there are some solid chunks left, but that's exactly what made the bread so good! This isn't your typical smooth batter bread - between the chunks of banana and the liberal sprinkling of miniature chocolate chips, it has character. And this character is quickly becoming a staple in my household.
Chunky Banana Bread
Lightly adapted from Alton Brown's I'm Just Here for More Food.
Weights are included with the measures because Alton Brown believes that accurate measurement creates consistency, and weight is the only truly accurate way to measure most ingredients.