There’s an openblas psi4 conda package available through the following command, so you can gauge the size savings. Be aware, though, of this issue. 400+ test cases are fine, including interaction energies with a variety of functionals (dft-bench-interaction). But there’s a lot of functionals messing up ionization energies with openblas, so I wouldn’t start production calcs just now.
conda create -n p4nomkl psi4 nomkl -c psi4/label/nomkl -c psi4/label/dev