Hi Sam,
Certainly the computational speed of OpenFAST will depend on the compiler and optimization settings you’ve used. I would normally recommend using an Intel compiler and O2 (maximum speed) optimization.
Independent of that, the computational expense will be impacted by the features you’ve enabled and the time step and number of corrections you’ve selected.
This topic has been discussed in prior forum topics, e.g. see: FAST Computation Time and Improvement - #10 by Jason.Jonkman.
Best regards,