You know i really enjoy helping people but there must be a million threads on this already, JUST BROWSE THROUGH THE TOPICS.
If you can't be bothered..
1/ All pickups sound similar through a Big Muff. It has NO transparent qualities, it would make zero difference if you use Filtertrons or EMG's.
2/ Hot Rails and the JB Jr are also similar, the Rails are slightly higher output i believe. Check sound samples on seymour duncans website.