Just to add yet more confirmation on it, BBPs are wound to around 8-8.4k at the neck and 8.3-8.8k at the bridge with
slightly mismatched coils and A5 magnets. The '57 Classic models all have A2 magnets are totally matched (at least within manufacturing tolerances) coils, with the plain Classic wound within 7.7-8.2k (Gibson specify 7.5k but I've never seen or even heard of a '57 Classic actually being that low) and the Plus version is wound to 8.1-8.5k.
Putting the stats aside and just listening to them, the Pros are always brighter and higher in power while the Classic/C+ set is kind of like an Alnico II Pro tone with just a tiny fraction more mids – slightly smoother and not quite as 'hollow' as fully-authentic PAF copies tend to be.
Really they're both appropriate for exactly the same kinds of music, mostly blues and classic rock but you can easily use them for country, jazz, pop and classic metal. I wouldn't use them for high-gain shredding myself, but then again, lots of people have done that with PAF-style pickups, so why not the BBP and 57s? They're general-purpose humbuckers, there's really nothing they're totally inappropriate for. Of the two I'd say the BBP is very slightly more versatile simply because it's a little more defined under very high gain and if you split any of them you'll find the BBP gives a more typical single coil sound, but it really is very close between them and it's not like you might love one and hate the other. Anyone who likes the BBP will probably like the 57s and vice-versa.
A couple of years ago I had a tough chat with Discharged (I didn't hear him around here lately) in regards with the unbalance coils of the Pros. He stated that, in his experience, there was no mismatch between the two coils. It is only advertised on the Gibson website.
In the case of the Pros, yes. They
are mismatched, but not by any more than you usually get within manufacturing tolerances. Less than 5%. So some people consider that to be 'matched', though it is, to nitpick, mismatched.
For the record, other pickups with the Burstbucker name are
far more mismatched, to the point where they often don't cancel hum very well and can almost sound like overwound P-90s. (Which is rather the point.)