The metal conduit would add a "shield" to interference to the LV wireing from the HV wires. So if you had metal conduit (as you said your HV wires would "The HV lines will run behind the OSB and into conduit, down into the box." but now that I re read it and look at your photos agian the conduit I am guessing would only be a very small section, I dont think it would benifit trying to change horses now.