veg room

i will be using 4 t8 4ft lights for up and down on the sides and i was gonna use a 400w mh for the top BUT someone gave me a 400w hps for free and i was wondering if i could use that for the top or do i need the mh?
is there any diff. between them both?

Standard MH is typically better for veg and standard HPS is better for flowering. Enhanced spectrum versions of either can perform better than a standard version of either bulb in all phases of growth.