I haven't chimed in on this thread for a while, but now that i've received over 550 hits on my YouTube video comparing Carvin's pickups, I suppose it's about time for an update.
The main difference that I noticed in the two sets of pickups was the larger dynamic range of the single coils. This is probably the reason that many of you preferred the J99A's for slapping. Slap bass typically has louder peaks than fingerstyle, pick, or tap playing.
jzucker's mp3 of the single-coil noise is a nice illustration of how bad the buzz problem can be...it's not just a matter of opinion.
One of the H50A pickups that I installed had a ground problem not related to my installation (according to the Carvin tech), so they had me send them back to the factory.
I opted to get a refund on the H50A's and re-install the J99A pickups. I might decide to try another stacked pickup in the future, but I'm very skeptical that any humbucker can deliver the same quality of tone.
No matter what the audience is hearing, I have to love the sound I'm producing in order to play my best. Sub-par tone is like having a pebble in my shoe that nags me for the first hour and drives me crazy by the fourth hour.
Same goes for the weight and balance of an instrument. If it isn't right FOR ME, then over time I'll be looking to make a change.
If Talkbass teaches us anything, it's that there are a gazillion basses on the market out there, so there's no reason to settle for an instrument that's not meeting YOUR standards.
As for me, I'm quite happy with my B50 still. I have found the 19mm spacing to be a more difficult adjustment than I expected, though.