I should have a blackstar fanboy sig... haha In the last year we've switched over our 4x8, three 4x4s, and the veg closet to led.
In my 4x4 I'm running a 500 watt blackstar over two 2x3 flood and drain tables. This light is built for 12 square foot area, and could probably do 16 or 20 with a light mover. Its penetrating so well that I'm giving some thought to growing out some landrace or near land race sativas in there and get some 6 footers. Not to mention the resin production increase from the UV! Not too sure if the buds make more resin (i'd assume so) but the leaves and stems are covered much more heavily on well known strains from HPS and outdoor. With a set of bubble bags and half a brain, this translates into much more hash from every harvest. I would venture out on a limb and say that some leaves are 10% THC or more
In the 4x8, we're running two 500s, but it's filled to the corners and they're not quite cutting it. Going to add a third, and since they only draw 66% of their wattage, three 500s comes out to 1000 watts power draw for 32 square feet of growing. With two lights, we've got the tent about 80% covered, so light 3 will be so intense that we'll have to raise them and/or buy a biiiig bottle of CaMg+.
In one 4x4 and the closet we are running a 240 veg models for our mothers and clones. They blow away T5s for growth and are so much less fiddly because you have a foot and a half useful range above the canopy rather than 2 inches. This translates into hardly ever having to mess with the height. The 240 veg is probably a solid 10 or maybe even 12 square feet of coverage because the plants don't require as much intensity in veg and it has a better spread.
And finally in the last 4x4 we have two 240 flowering models. These aren't quite cutting it for this area, so we're either thinking of buying a third or maybe trying the 135 watt circle.