Hi
They're pretty similar to each other - I've got a couple of stormy mondays (In a PRS Hollowbody and a Gibby 175) and a PG Blues set (in a Les Paul). I would say (although it could be the difference in the guitars of course) that the PG Blues is a little brighter than the Stormy Monday, comparing the bridge pickups. They're both great - of you like, I'll do a head to head comparison - what sort of style do you play?
Comparing to a 57 classic, they're both slightly underwound I think, so will sound more open and dynamic. The 57 classic is also potted, whereas both the BKPs are available unpotted (which I prefer). I actually swapped the 57s out of my gibson for the BKP stormy mondays - the BKPs are way better IMHO