Disclaimer - I've not bulk traded since Engineers update so I could be a bit off on this but previously:-
Imperial Systems. Best profit was on Imp Slaves / Indium or Berylium routes and up to 4.5k pt. you needed to find Agri/Industrial economy on Torval control for slaves the a recurring Extraction/Refinery economy not in Torval control to get the metals.
Independents and Federation, best profits between Progenitor Cells and Platinum routes.
Now add in boom and bust states for the most profitable commodity. Buy at Bust and sell at Boom. Your return leg will suffer the boom to bust modifier so take the cheeper commodity back, assuming an A-B to B-A type route.
So your holy grail, Bust Agri / Industrial in Torval control to Boom Extraction / Refinery not in Torval control. Preferably under 12ly apart with less than 500ls to station.
If you find that combo be sure to also stock up on rocking horse poop, hens teeth and give Elvis a lift home.
Outpost can return higher profit if your getting started as they can't be farmed out by TradaConda wings. Supply and price drops rapidly when big ships start moving 500t per trip on a frequent basis. We also share the background trade sim with the PC boys and they can negatively affect our XB trading.
PM me if you want some starter systems in Imp space to get you going.
Fly safe CMDR.