A friend gave me an 8qt pressure cooker from the 1960's. I decided to use it despite dire online cautions. I have no manual for it and some of the guidelines are hard to interpret. I failed to keep good notes at first but am now doing so.
FWIW: a pound of supermarket dry kidney beans, soaked overnight in salted water, rinsed, covered to a depth of 1" by fresh water and a glug of oil. 15 min at pressure, 30 min natural release yielded overcooked beans. A pound of supermarket dry great northern beans, same treatment, 5 min at pressure, 15 min natural release also produced overcooked beans.
The brining of the dried beans, as recommended by the Cooks Illustrated people, definitely does a good job at flavoring the beans. This seems to make them cook faster, in contrast to salting the cooking water, which makes for tougher skins and harder beans.