With precast, your loads are applied from both sides. Negative moment on the face of the panel during stripping, both positive and negative moments on the face of the panel during wind pressure and wind suction, and don't forget shipping and handling. Try to push the architect for a thickness that will allow you to double reiforce the panel. You can do this by referencing the PCI manual. Typically with precast, specs. will require an uncracked section. We all know that reinforcement is useless unless the panel cracks, and with precast, cracking stress is lowered to 5*sqrt. fc'. Good luck.
