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+1 on temperature, winding tension (that can further stretch and thin the wire), magnets, pickup height setting, wire variation from the factory spool.
+1 a "One kohm" range is audible given using the exact same Pots 'n Caps (and that means physically the exact same ones, pots range by 20% and so two guitars can sound vastly different .. usually leaving players to assume it's "the tone wood!"), same pickup height settings, strings, etc.
The 1kohm difference is the performance characteristic of vintage Strat pickups (5.5kohms) vs modern (6.5kohms) vs Mustang/Tele/Duosonic pickups at 7.5kohms (yes, Tele has some geometry differences and sometimes a steel baseplate).
You can adjust pickup heights and wipe out a lot of the differences, easily. If you are playing with more distortion than clean you can wipe out a lot of variation.
I avoid the companies who try to convince pickup buyers to use their unlabeled charts for Bass/Mids/Treble rather than concrete measurements. All pickups should have measurements and a tolerance range (even if it's scary wide -- work on fixing that 'Mr Factory' that's what Quality is) just like every other manufactured product out there.
Imagine if the pack of strings you bought said "these are Rock strings, you'll get some bass, some mids, and some treble while they may be too hard to bend or too squishy to stay in tune, you'll like them" Rather than showing "0.009", "0.010", and so on. Or your picks never showed "Heavy 1.2mm" and instead gave you a chart "you'll sound like BB King, Jeff Beck, or the Nickelback guys".
On similar pickups, same geometry, close kohms, same magnets, and wire/coating I've found the biggest variation to tone is how they are wound and the resulting internal capacitance. A pickup's capacitance alters if it will sound clear and articulate or muddy and muffled that you can't turn the tone knob enough.
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