If you wire the light to run on 240v it will cut the amperage load close to half. Either way you should get a higher amperage service, at least 100 amps.
I am still in the planning phase and I was wondering if it is worth the trouble of getting a mag ballast and using a cmh or just getting a hps grow bulb. Please share your experience if you have actually done this not just what you think from what you have read online.