Typical lighting requirement is 400-500 watts per square meter during flowering. Sativas usually require a bit more, indicas a bit less.

Spectrum isn't as relevant for HID lighting since they don't actually release a continuous spectrum like fluorescent lighting. However, the bluer MH lighting will make plants stretch less than the redder HPS light. This is generally a very good thing, since you don't want your plants to get too tall and lanky.

A 600 watt light will produce about 600 watts of heat. How hot this will make your grow room depends on the size and ventilation of your grow room.