The Nailbombs are good powerful all rounders although they'd suit the LP better I'd say - have a listen to the clips!
As for 52/50mm spacing, that's the string spread at the bridge, the distance from high E to low E, get the pickup that's the closest match.
Calibrated set means that you'll get a pair of pickups wound to give complementary tones and good volume balance between neck and bridge positions.