There's a lot of discussion here:
Who has WARWICKS with non-MEC pickups? although not a lot regarding Stage II's I'm afraid.
Generally, folks go with one of three choices for their Warwicks; it depends what kind of slap tone you're after: if you want dark and moody, Barts would be a good choice; if you want bright and zingy, maybe EMGs would be a good start? SDs seem to be the third popular choice, for a more traditional sound.
I'm waiting for a Nordstrand to go in my Streamer Jazzman, for pretty much the same reason as you: my slap sound is currently very muted and compressed in the upper register, leaving things very clanky with no zing. Nordies aren't an obvious choice for a Warwick mod, but seeing as it's an MM pickup I'm replacing, it seemed a good way of getting closer to a Stingray tone. Other guys around here have put Nordies in their Warwicks too and seem to be very happy with them. Personally I just can't wait til it arrives and I'll know for sure whether it's an improvement
FWIW, One thing that seems to be a trend talking to folks round here is that people seem either seem to love the MECs in their Warwicks, or think that almost anything would be an improvement. I've played MEC equipped Warwick's that have blown me away tone-wise, and others that sound dreadful.
