Well the 250k pot came and is installed. I thought I'd ordered a linear pot but it turned out to be a log one, and a log was was what I actually wanted, as I always got the actions of log and linear pots confused in tome controls. On a linear 500k pot, I was getting 250k at the mid point of the track between the two normal connection lugs, and 98k at 50% with the log pot.
The 250k log pot is better but still not ideal as most of the action is still occurring below 5, though it does happen more controllable. So what I ideally want is a log pot with more of a curve, so that I get 10% of the pot's resistance at 50% travel rather than 20% of the pot's resistance. And I probably won't get one of those before Wednesday, so it will stay like it is, but I'll note it for future reference.
So in theory:
Audio taper tone = quicker tone roll off
Linear taper Tone = slower tone roll off with more tone roll off at the lower settings.
(If I keep writing it down I may remember it correctly one day).
But certainly with this pickup and capacitor combination, there wasn't a huge amount of audible difference between the linear and log pots. The resistance value required too start hearing some treble roll off is pretty low, so the audio pot is in is more gentle part of the resistance slope by the time it gets there, so it acts in a similar way to a linear pot. There is a small difference between the two, but not a huge amount.
I'll have to do some proper testing.