Just my $.02 worth.... the neck pickup alone on a Jazz Bass can - *depending on the Jazz Bass in question (pickups/preamp, etc.)* - get you close enough to a P-Bass tone with a little extra EQ'ing and adjustment of the tone control. I love my P-Bass live and in the studio, but a P can't do a 'Jazz Bass with both pickups dimed' tone... but the J can get you in the ballpark of the P-Bass. I could see preferring a Jazz Bass live just for the added versatility. I have a Classic Vibe 60's Jazz Bass and have found the neck pickup soloed to be growly and 'P-Bass like' in enough live situations to only make me bring that one bass. The audience won't know or care really, and your sound guy will appreciate just having to do minor tweaks to the FOH.