The custom to me, is harsh. It has too much edge. Good for pick scrapes lol! Pro'lly the ceramic thing. I see a lot of people dis' the JB pickup. If they understand what it is, they shouldn't. That pickup is a dominant LEAD pickup. It has a lot of mids, especially high mids which make single strings sound thick. If chuggin' on the E string is your thing, most don't like the JB. If you like fat leads, the JB may work.
I loved the JB in the Brian Moore I had. It had such a singy, lead quality. But it's hard on your ears after awhile. ESPECIALLY if you use V30 speakers. too much upper mids.
But put a JB in an alder body and be prepared for a headache. It's like someone breaking beer bottle after beer bottle in your ear. CLANK CLANK. I had that pickup in an alder body for a day and that's all it took. Ohhhh the most awful tone. IMO, It needs a dark guitar like a Les Paul or something with mahogany or maybe basswood.
Gibson 57's are very nice stock pickups btw. They are so balanced.