you wont be able to tell the diffference.... trust me.... if you do decide on an upgraded bridge, keep in mind that the bridge (by its thicker bass plate) will take the strings higher... on a jazz bass you can bottom out the saddles.. i once thought about a bridge upgrade but realised the difference is very minimal...
your money would be better spent on great strings, or pickups... imo... put some Lindy Fralin's in your P Bass, and hear it sing...