Choosing A TB For A Magnum

so i broke down and bought the hughes/eddy intake for my 5.9L magnum, anyways im working on building this truck for mpg but to be able to tow (its not a diesel, and dont plan on buying one). My biggest stumble is the throttle body, what CFM is to much??

5.9L Magnum
Stock TB (for now)
Hughes/Eddy intake
Stock Injectors
Stock Long block
Stock Exh (plan is shorty headers, 2.5" head pipes into flowmaster Y pipe, cat delete, flowmaster super 50 delta)
Stock Cam (Crower Hyd Roller Coming soon CRO-34418)