The Costs and Revenue for each Contract is dependent upon the Locomotive & Boxcars used to complete the Contract. I.e., Locomotive Costs + Costs for each Carriage attached determine Total Cost with respective, cumulative Revenues.
Experience earned is based strictly upon the Level of Contract and is unaffected by any other variables.
The Time required to complete each Contract is dependent on the Locomotive's Speed & Level of Route taken to Transport Stone to the City.
While a Locomotive's Efficiency may affect the DefaultLocomotive Costs below, Carriage Costs are consistent and remain set, regardless.