A rotor blade for a turbine of a combustion turbine engine having an airfoil that includes a pressure and a suction sidewall defining an outer periphery and a tip portion defining an outer radial end. The tip portion includes a rail that defines a tip cavity. The airfoil includes an interior cooling passage configured to circulate coolant. The rotor blade further includes: a slotted portion of the rail; and at least one film cooling outlet disposed within at least one of the pressure sidewall and the suction sidewall of the airfoil. The film cooling outlet includes a position that is adjacent to the tip portion and in proximity to the slotted portion of the rail.