Re: 250k pot for JB...
I have a late '90s G&L ASAT Deluxe with the '59/TB-4 set. Maple over mahogany, V, T, 3-way selector and global coil cut. It has 250K pots.
I like this set, a lot. I'm a classic rock, blues, country, jazz guy in a G/B/K/D cover band . I don't use a lot of crunch rhythms, or metal. I use Mesa amps, but even on my lead channel solos, I only have the gain 6-7. I usually gig with multiple guitars.
Some guys complain about the shrill upper mids of the JB, but I'm not getting that here. It is warm, fat, rounded--a good rock tone. Very similar to the Classic '57+ bridge pickups I have in a couple of my Les Pauls. (I'm sure they have 300K pots.) The ASAT does not sound like a Les Paul to me. The coil splits do not make it sound like a Tele, but it is a usable tone on both pickups. It does not "twang". I will usually set the amp up for the split coil; then when I use the HB mode I have a nice little boost and HB fatness. The '59 is not too dark with this setup; sounds like a vintage humbucker to me.
From my experience, and from what the other guys on the board have written about the JB, I think the 250K pot is a good place to start--and adjust from there.
Good luck.
Bill