Neither of those two will exhibit single coil hum. The nj5s will sound like a Jazz pickup. It will be more focused and have more growl when solo'd and you dig in. The split will sound more like a soapbar. Less growl and a thicker fuller response. If you like the way your P sounds already, going with the J pickup is pretty common. It will add a some high mids that the P pickup doesn't have. If you find that you are thinking you need a fuller tone, then try out the split.
I'd opt for the J pickup. If it doesn't work, you can always route out further for the split. If you go with the split to start with, you can't really unroute your bass to go with the smaller J.
Not positive, but I think the dual coils would let you install a switch for various coil tapping possibilities too. Won't sound as J like as a J pickup, but would offer a soapbar and a J'esque tone all in one pickup.