Deriving Minimum Efficiency Requirements for Baseline Chillers

We are wondering how to interpret the Minimum Efficiency Tables of Chapter 6.8 in ASHRAE 90.1-2007 to model HVAC efficiencies of baseline equipment. Our baseline building has a floor area > 150.000 ft² so we selected a chilled water system and a cooling load greater than 300 tons so we selected two equally sized water cooled screw chillers. For 320 tons the chillers are sized 160 tons each. What should be the COP of this two chillers according to Table 6.8.1C? Should it be 5.55 according to the equipments size or should it be 6.10 according to the cooling load of the building? In general what is the meaning of size category in this tables, the building load or the equipment size.