I am absolutely in love with the lights being vertical.. I think a single 600 in a 3x3 would be the best.. Im thinking about seperating the 600s and hanging them beside each other instead of stacked.. Stacked is great for taller plants, but side by side is the best for smaller plants..
in a 4x8 i would do two seperate circles in the tent. each circle would have a single 1k watt..
so like this
xxxx xxxx
x o x x o x
xxxxx xxxx
x's are plants around the bulb..
Or...
you could go with long boards going up horizontally on the wall holding different tiers, for a stadium.. but i guess it depends on where the door is, what ur comfortable with,etc.