and remember fender used to make many different necks for the p bass, like u-shape, c-shape, v-shape, etc, and all of these necks would have slightly different masses, possibly the same difference in mass between regular modern day p and jazz necks. by the way, i am not trying to start an argument here, i'm just curious about how this could possibly affect the tone that much. and trying to help the o.p. with his question. joash, i don't think anyone would be able to tell if your p/j bass was not a p bass if you soloed the p pickup, no matter what neck is on it unless you told them. does anybody reading this think they could tell in a "blind hearing test" whether a p bass had a jazz or precision neck on it?