I have a Euro 6" for my 400w, and I like it. I have mounted mine to the top of the box which gives me more height (mine is only 4' high also
) and keeps more heat out. I like your idea for mounting both 150's in there as my 400 is a tad too much (9,166 lumens/sqft), at least directly below the bulb @ ~10".
I have started using a Botanicare (grow and bloom are I think the power series, liquid karma, blast off, sweet, cal-mag and Blue Mountain Organics SPT, all at basically 1/2 strength. I switched from Fox Farm mid grow after my buddy trading me samples for cuttings. So I can not say from my own experience (only last 3 weeks) but my buddy's garden is very nice. Very thick stalks and tight bushy growth in coco/perlite and 1000w.
The product claims you can not burn your plants with it and recomends using EVERY watering. My buddy does this and has for some time. His plants show no deficiencies or stress. The coco holds so much air, he can keep the top of the soil constantly moist and with the help of mychrozae(sp) has a mesh of tiny roots all over the top of the coco. He likes to add a little nute solution twice a day, about a pint each in 2 or 2.5 gal of medium in 3 gal grow bags.
I have not fully switched to coco yet so I do not water daily, but I have started to use every watering (nervous as hell after the 1st gro/nute burn)
I am not recommending this to anyone yet...I am trying it as I trust my friend and his 15 years of experience, but things look pretty good.
Good luck on your upcoming harvest, it looks like your nugs will not suffer from the burn, looks nice!