WOW m8 no need for that attitude more ppl cant spell than can spell! if you pick out stupid shit like that then you are sad as fuck!
a 600w will grow you mor bud than a 400w with very little extra heat, a 600 is almost twice as efective as a 400w hps.
iv used 400, 600, 1000s i love 1000s in the winter and i have to use 600s in the summer
throw the 400s in the bin they just dont give the bang to get fat arse buts like the 600s and no where near a 1000w hps.
at the end of the day how much d you want to grow? if you smoke your self then a 400 will supply you all you will ever need every 2 months.