In general a very powerfull pickup will sound better running through lots of gain than not. A weak pickup is still tonefull under high gain, but perhaps not pleasing in a metal sound sort of a way.
The reason is that powerfull pickups use longer peices of wire, which tend to attenuate highs more noticably, and the sound is normally less detailed and dynamic. This is fine for a tonne of gain, but you notice it much more in cleans. However, powerfull pickups also tend to have a more pronounced attack to the sound, which gives heavy riffing and fast lead focus and punch. Weak pickups dont do that to the same extent (though the majority of this is in the way you play: the pickup can help! Espesially if you want to play something that needs a lighter touch and precision, but you want it to sound in-your-face)
It has to be said, though, that BKs powerfull pickups, right up the the C-Pig, are still very useable for cleaner sounds, and I often find my warpig in particular and C-Pig in parallel to be better than many more common pickups, naming no names *cough*DUNCAN*cough* for cleaner sounds. They still have more life, responsiveness and depth. Also, crawler bridge is a freak for this: medium-high power and can achieve vintage sounds and entry level capital-M Metal (to me thats metallica, megadeth et al) with equal aplomb.
