Re: Sonic differences in the custom series?
A2 (the Custom Custom) THICK sounding. Lots of lows of low mids with slightly muffled highs. Pretty chewy attack but with lot of sustain. For rhythm guitar for hard rock, I like this one for providing very very thick power chords that leave room in the mix for a lead guitar.
A3: brighter like a custom 5, but with less bass and less output. Punchy, but doesn't drive the amp as well as anything else in the custom series.
A5 (Custom 5): Big bass and treble, with scooped mids. More punch than the Custom Custom. If you don't use this in a midrangey guitar, you may be lost in the mix. If you like the 59b, you might like the C5.
Ceramic (Custom): there are reviews everywhere of the stock custom. Somehow I never have ceramic magnets so I've never tried this one!
A8 (Custom 8): take the thick mids from the CC, the bass from the C5 (but a little chewier), and the treble is between both. It's big, bold, and has an aggressive grind, with lots of output and sustain. The custom series already feels "hot" to me (I usually go for PAF types) but the C8 has even more ability to drive the amp than the CC or C5. It's a great pickup for if you want some modern tones with a little softer attack and a little less edginess than high output ceramics.