I'm a recent (about 5 years ago) convert to D'Addario Helicore after playing a friend's bass. They make 3 versions, Orchestral, Hybrid and Pizzicato. If I've understood their blurb correctly, they're the same construction but with more or less damping depending on what kind of playing/sustain you're after. I've just gone from Hybrid - Brill generally- to Pizzicato- all the sustain and growl you could want, in fact I have to keep it under control sometimes! Still grand for bowing, but I'm doing that in a song context rather than Orchestral. I don't do the rockabilly slap, but for the bassline with percussive accents they're spot on.
If anyone fancies a go ill be playing at Norwich, Bristol and Bingham over the next couple of weeks with Steve Tilston.