I just recently put the bart 9J S/SB set into my MIM jazz. Here is what I think:
The pickups sound more round and modern than the stock pickups. They have less of the characteristic J-bass snarl, for better or worse. (but it still sounds like a J-bass) There is definately a lot less noise also, as these are split coil pickups wound to match versus the stock single coils which at least on my older MIM are both wound the same way.
I'm really happy with them though; I find its easier for me to get a consistent, thick, punchy sound. A bit of this is just because of the reduced noise floor enabling me to dial in higher gain settings on the amp, but the tone of these pickups is genuinely smoother than the stock pickups.
They are noticably quieter (as in lower output) than the stock pickups. Even more so versus the uber-loud Dimarzio Model
Js in my other bass. But this is easily resolved by turning up the input gain on your amp a little bit.
I like 'em.