Herein we have tested the complete PNO space extrapolation approach as a lowcost way of altering the accuracy and efficiency of DLPNO-CCSD(T 1 ), so that it can be used to calculate reference values for benchmarking enzymatically catalyzed reactions. For this we have used a test set of 10 REs and 4 BHs representing both organic and metalloenzymes, taken from previous benchmark studies for which DLPNO-CCSD(T 1/0 )/TightPNO references had been used. CPS (5,6) extrapolated results approach the accuracy of TightPNO (which has a default value of T CutP N O = 10 -7 ) but do not fully replicate it; similarly CPS(6,7) approaches results calculated with a tightened T CutP N O value of 10 -8 , surpassing TightPNO with only the additional cost of the much more efficient T CutP N O = 10 -6 calculation. Using these three levels of theory as benchmarks to test DFAs, we see only minor changes in the MADs with the reference quality. The effect is more significant for the metalloenzymes, but even with changes of up to 0.5 kcal/mol in the MADs with each step up in the reference level of theory, there are only few significant changes in the relative rankings of the DFAs. To further investigate the results for models of organic enzymes, for which the differences in the MADs appeared to be negligible, we extend the analysis to the ENZYMES22 set of enzymatically catalyzed reactions. Even across this larger set we see no significant difference in the benchmarking outcomes across the three tested reference levels of theory. We therefore conclude that the CPS extrapolation technique can be useful for calculating reference REs and BHs associated with enzyme active site modelsparticularly in the case of CPS (5,6), which gives similar results to standard TightPNO at a significantly reduced cost, allowing DLPNO-CCSD(T) to be used as a benchmark level of theory for larger systems. We also present the final DLPNO-CCSD(T 1 )/CPS(6,7)/CBS (3,4) REs and BHs to be used as updated reference values for the ENZYMES22 set in further benchmarking work.