The 'truest' indication of performance deficit or surplus is measured based on EAS - even though your stall speed will be published in IAS, it is the EAS that matters.
Well, no. EAS is relevant only as long as the air can be considered to be incompressible, i.e. at low Mach numbers.
CAS is greater than EAS because the pressure in the pitot is higher than it would be in incompressible flow. The compressibility that causes CAS to be higher than EAS affects all aerodynamic pressures that keep the airplane in the air.