if only one bulb may be purchased, i;d take this, i think
http://www.buylighting.com/450-Watt-Self-Ballasted-Mercury-Vapor-Lamp-p/sbmv450120.htm
of the 2 you've posted...
i'd get the 400 mh
i'd use it to crack, veg, clone, and sex my 10-12 plants (4-7 males will phase out prior to flower)
by the time i had done all this...
5 days germ/break surface
15 day seedling
15 day veg
10 day root cuttings
5 - 10 days sexing...
you ganna tell me that if i buy a mh400 watter now, i can;t come up with a hps 600watter(IDEAL for a hobby grower) in 8 - 9 WEEKS time?
i can't save 15-18 dollars per week while i'm staying at home watching my girls get all sextyfied?
you don't need the hps till you need it - get the mh 400