Do a search for air cooled reflectors. They are built to be connected to ducts to get rid of the hot air they produce. There is a piece of glass between the bulb and your plants so the hot air doesn't escape. Just do a search for air cooled reflector and you will see what they are.
In the near future, I will be running 2 600watt lights in a 4'x4' area. You could cover a 4'x6' area ok with those lights as well. But the more lumens/watts per sq foot, the tighter your buds will be. My 600watt light is not quite enough for my 4'x4' area. Another one in there, or even a 400watt light, would increase my yield by quite a bit. So for your best coverage with the 2 600watters, I would say a nice 4'x4' area. Stick like 16 plants in there, hit 1/2 gram per watt and you got yourself like 1 1/2 lbs. And the 2 600watt lights will give you a much better yield than one 1000watt light in the same space.
You can do larger areas, your buds will just not get as dense. You would probably be able to yield the same amount in the smaller area with less plants simply because the buds are denser and they will be able to get better buds lower on the plants.
I like to have as many lumens per sq ft as possible. For the past couple of years I have grown at 75-100watts per sq ft, and love it. If you can keep it cool, this is the way to go. RIght now I am well below this, simply because I wanted to build a new room, but don't quite have the money for the second light yet. But it will be up by the end of this harvest.
I was growing in a 3'x2' cab with my 600watt light and was getting like 11oz every 60days. This is with 4 plants in a 6sq ft area. With my 400watt light in 2'x2' area with 4 plants, I was getting like 6oz every 60days, and when I moved the 400watt light to the 3'x2' cab, I ended up with almost 8oz off of 7 plants. I don't think going any bigger with the 400watt light would have helped yeild. My yeild per plant went down, but because I was able to fit more plants, I was able to yield more. But the buds were noticably less dense.