Good thread.
Like Twinfan I prefer hotter pickups for classic rock and metal.
I've used low output, medium output and high output BKP's and they were all good for what they did. The lower output models (especially the ones with AIV neck pickups #Mules/Mississippi Queen) sound more woody and open, which makes up for a 'bigger' clean tone thats especially great for blues and jazz (think 'Need your love so bad'). However, most of this 'bigness' has to do with the guitar as well (Les Paul in this case). Yeah, you really want to play blues with low output BKP pickups, at least I do. The hotter these pickups become, the more compressed the tone becomes.
BUT, in many ways you'll always have the tone you had before, no matter if you're using Mules or Painkillers (ok, that's kind of an extreme comparison, but still)...remember it's the guitar that has the tone, not the pickups. We should know that pickups have an influence on the tonal balance (certain frequenties) of the guitar, but they don't really change the tonal characteristics of the guitar. It the guitar wants to bite or scream, it will always do that (no matter if you're using Mississippi Queens or Rebel Yells). That's a tonal character the guitar has or not. For one particular Les Paul I went from Mules to Rebel Yells, to Holydivers and finally to Cold Sweats. They fit the guitar like a champ and they do exactly what I want them to do, no matter if it's clean or distorted. The guitar just needed that extra output (and probably the ceramic magnet in the bridge) to sound at its best and it's a great screaming LP tone that's still open and sensitive to your playing. It sounds warmer and more fluid in the neck position. Some amazing pickups just fight with a particular guitar, it's just the way it works. Rolling down the volume knob can easily give that classic attitude with the higher output models, depending on the guitar as well.