6x5x4 room 400 watts

ive got 6 plants (white rhino) under a 400 watt hps light and im thinking about upgrading lights, what would be better,

A= buy a new 600 hps for the room size above or
B= add a 250 hps which ive already got, and have the 400 and 250 in the room and make sure i keep rotateing the plants.

p.s is the 400 really enough for 6 plants? ( i dont think so)

would 650 watts of light plus 8" rvk fan, and 4$ inline fan and 2 oscilation fans luck like a high amount of electric? (in the uk)
thanks for any help.

a 600 watt alone is not gonna be enough for that room

I would concur. With one 400w I struggle with a 3 x 3 area, 2.5 x 2.5 seems more adequate for the lighting. Which works out to 4 plants, with a better hood I might see better results. You could partition off a smaller area if you are worried about electricity.