No doubt you will want to hang me high from the yardarm after this, but here goes.
Looking at Jazz bass single coil pickups. Randomly picked examples.
Nordstrand NJ4 £140.
Lindy Fralin Jazz Bass £150
Tonerider Jazz plus £58.90
Nordstrand blurb:
Made with 60s era correct Heavy Formvar wire and Alnico V magnets. In winding these pickups we use a simulated hand wound pattern.
Coil resistance ~8K
Lindy Fralin blurb:
Using ALNICO V magnets and 42 gauge Heavy Formvar wire, they are all hand wound to vintage specifications.
Coil resistance ~8K
Tonerider blurb:
High-Grade "Smooth-Top" Alnico V Pole pieces - no sharp edges!
42 gauge Heavy Formvar wire
All coils scatter wound on our 999-step CNC winding machines.
Coil resistance ~8K
The parameters from a pickup that matter are output voltage and frequency response.
The output voltage depends on the magnet dimensions and field strength, the wire diameter and number of turns on the coil. The frequency response depends on the inductance of the coil.
If the magnetic field is too strong, it will influence the string and reduce the sustain of the guitar. If it is to weak, the output level will be low.
So there is an optimum field strength to aim for.
The greater the number of turns on the coil, the greater the coil resistance, the higher the output voltage.
The greater the number of turns on the coil, the higher the inductance of the coil, reducing the high frequency response. A compromise between output and frequency response.
So there is an optimum number of turns to aim for.
Three makes of pickup, all with the same physical dimensions.
All use Alnico V pole pieces of the same diameter with similar field strengths.
All use 42 gauge wire with similar number of turns.
All use simulated hand wound patterns.
It is a basic electronic component, magnets and wire, a coil, no magic involved.
How much difference in sound could there possibly be?
Can one sound sweeter? How?
Could you tell the difference in a blind listening test?
Is this a case of the Emperors new clothes?
Different output levels? Doesn't matter, plug into an amp and adjust the gain.
Different frequency response? Doesn't matter, plug into an amp and adjust the tone controls.
So, you got to ask yourself, where's the best bang for your buck?