I have an NS SF-I and an NS SF-II and played through the exact same rig with the exact same EQ settings, the SF-II (with the bridge pup only selected and the vol/tone knobs on the bass set the same) does not sound identical to the SF-I. Close, but there is a perceptible difference. In a busy mix and/or to anyone but me, it probably amounts to splitting hairs.
Is there more material in the SF-I center block? Are the tapers of the tone pots slightly different? Is it due to a tone wood density variation? I don't know.
Just sayin'...
the Bridge pickup on a SF-1 bass vs. the bridge pickup on a SF-2 bass is a completely different conversation, than a Bridge SF-1 vs a Neck SF-1, on several levels.
I was suggesting for those passionate about this discussion of the SF-1 basses, to try the neck and bridge pickups on the same bass (a SF-2) as "additionally recommended research" just as another control group/variable, however you classify it.
A SF-2 bass is a lot heavier with all that extra hardware and that has some effect on tone. also the neck pickup is still pulling signal from the strings, even if u have it switched off and its volume all the way down (you are just muting it), so the SF-1 has the full string signal at all times (u would need the SF-2 bass in the middle position with both pickups activated to achieve this). I am actually much more of a single pickup person, guitars like Jetstar and LP Jr, and most basses like the P-bass and mustang only have one pickup. But with the Guild Bisonic basses, the SF-2's ive experienced just seem like the perfect SF bass. I've also heard some SF-1's that really sound unreal, no doubt the player is the biggest factor- but those were all neck pickup SF-1's.
one thing I am pretty sure I have figured out even with all of the possible unknowns and variations, I like the bridge pickup of the mahogany SF bass better than the bridge pickup of the maple SF Bass (the mahogany bridge pickup sounds more like the maple neck pickup). the mahogany neck pickup is the darkest tone of all (in a very good way), all other things equal (which again, more likely there is some circuitry variation among them, than not). the solid body mahogany JS-2 bass with the neck Bisonic is all kinds of darkness ("Luuke i am your father!"), but that one also has a super treble-ee mini humbuker in the bridge, and almost certain the neck tone pot is 250K (and bridge pot 500K) the earlier Jetstar (mahogany) with bridge Bisonic only, has more treble ( but is also likely a 500K tone pot?).