There's a lot of confusion surrounding pickups, the sound they create and their impedance. I'll try to keep this as simple as possible for you because there really is a great deal of baffling psycho babble going on between the different manufacturers, however staring out by taking their word for the type of sound you might get out of any particular pickup may be an OK approach but many other factors can influence the sound you get from a pickup. Like your guitar, amp, effects chain, speakers, even the type of cables you use can all have a positive or negative affect on your sound and that's when you become disappointed because you didn't get the sound the manufacturer had promised you. I've provided links below to some of the better known pickup manufacturers. Go ahead and check them out if you're curious.
A few words about impedance - Impedance - im-'pëd-ens - n: the opposition in an electrical circuit to the flow of alternating current.
The basic rule to your pickup's impedance is this: The higher the value - the higher the output or the "hotter" the signal. Impedance is measured in ohms. Let's look at some examples of this... Most of you are familiar with the Fender Stratocaster, The Gibson Les Paul Standard, and some kind of hot rod guitar like say a Jackson or maybe an Ibanez. Ok ! The strat is about 6Kohms (six thousand ohms) - the Les Paul Standard is right around 8K - while some of the hotter pick ups can be anywhere from 12K to, believe it or not..24K ohms
Just because a pickups output is higher doesn't necessarily mean it will be distorted when you play through a clean signal, although it will have an effect on your clean sound, but what it does mean is when you apply some distortion, fuzz or overdrive you'll get a lot more out of it.
I hope this helps clear the air a little and take some of the mystery and confusion away from choosing a pickup. I could go on to write volumes on this subject but most of it is available through the links provided below.
" pic long & prosper " Lightning Joe