Greg:
From memory, HPS had a lower 'running' current after warm up; MH was the opposite.
There are 360 watt MH lamps, which were supposed to retro the 400 fixtures for 'energy saving'. I do not know what this did/does to the operating load. Comparative math (seat of the pants style) 10% reduction in lamp wattage should equate to 10% on line side of ballast; 460 -46 = 414.
Time to do the upsell to T5 fluorescents, or better yet LED with 100k hr life. ROI is quick too.