If you are going to change everything you might as well go to HPS if colour is not an issue.. I believe the "lumens per watt" is greater for HPS than metal halide or old school mercury...
Also, double check your input voltage.. I once put a ballast in a fixture that was labelled " 230V". and had a " 115 / 230V" dual rated ballast.. too bad for me the input WAS 600V!
it looked spectacular for about 6 seconds when everything was turned on! [Linked Image]