If this Installation is for Service Feeders (from a Poco Transformer to Service Equipment), you need to verify the requirements with the Service Planner before bidding this Project (or before commencing the actual work!)
If the Installation is on the LOAD side of the Service Disconnect, then (6) 4" Ducts with 4-750MCM CU. per duct is sufficient... if NO Equipment Grounding Conductors are installed!
If an EGC is to be installed, that will be a minimum of (1) 350MCM CU. per duct, so now the Ducts would be 5" (???)