well, if there was a point to my post, it was that either one will do a pretty good job all the way thru. theres alot of other variables so idk. i do a single 600 hps vert atm and im happy with it. if i add a second light it will be a mh stacked on top. as far as wether 2x400 is better than 1k idk it kind of depends on how you go about it. 1k bulbs def have less problems getting good density than 400's if thats something that matters to you. 2x400 would have a bit better coverage but its still less light than a 1k. idk much about cmh ive heard good things but no personal exp.
as far as the yield thing... i think the reason alot of ppl like mh for veg is that it reduces stretch. tighter internodes means shorter plants and, probably, denser buds. if you keep your plants happy thru the whole grow, you will get better yields. if you dont keep them happy, no light, nute, additive, system, whatever will do much good. so wether or not its worth it idk, prob not if your just starting. you will prob go thru several dif lights and set ups before you find one you like, and there is literaly no end to the amount of crap you can waste money on growing weed. lol im realy stoned
hf