I find these kinds of questions (the B string on one type of bass vs the B string on another) interesting but difficult to answer in any conclusive way (other than saying than it's unlikely any B string will sound very good above the 12th fret

). With relatively few exceptions, most of us TB contributors have quite small sample sizes from which to draw our conclusions. Yet we tend to be quick to generalize, even after only trying one or two of a specific type of bass. Of the five string basses I've owned, the ones with the best sounding B strings have probably been my main Lull M5V (I haven't spent enough time with my new Lull to be able to say for sure - but so far so good), which is 35" and my Sadowsky Modern, which is 34". I suspect that the main reason the Sadowsky sounds as good as it does is because of the pickup placement (which makes for a tighter, more focused sound all around). It also shares the same type of string (DR Hi-Beams 40-120) as my Lull, so that probably makes a difference. Having said that, none of the Sadowsky Jazzes I've owned or played (all NYC) had B strings which sounded as good as the B on my Lull or Modern. Only one of those basses was strung with DR Hi-Beams, and all had a heavier gauge (45 -130). The MTD 535s I've owned have all had decent Bs - but not as good as the Lull or Modern's Bs. Again, however, the string make and gauge were different (hex core, 45-135). The B on my 34" MTD Saratoga is just as good as the B on the 535s. The B's on my Rob Allen, Status and Modulus have also been good (though I still think my Lull has the edge over those basses).
All of the above might also depend on how my amp is EQ'd and the room I'm in. Lots of variables. My new M5V sounds very different from my other M5V and, preamp aside (assuming a relatively neutral sound is being produced in passive mode), the only spec difference is the fretboard wood and any possible difference in the pickups (despite them being labelled the same: custom wound SD singles). If I was going to order a five string Lull with the aim of getting the most useable B string possible, I'd go with the theory and order a 35" (there's a reason the shop recommends 35" for their fivers) but it could very well be that the best B to ever come out of the Lull shop was a 34". Something that I don't think has been discussed here yet is top loading vs through-body stringing of the B and whether or not people have found that makes a difference to the sound of the B (I have never experimented where that's concerned).