i also use the 400 HPS for both veg and flowering, i could do without the big ass fan leaves though. my stems are really thick and my lil buds are coming along nicely. no pics though unfortunately. I'm sure that if you only have access to one spectrum HPS is the way to go.
HPS is fine for veg. It creates taller plants with long shoots, compared to an MH which will keep the node spacing a little tighter and keep them a bit shorter.