As long as you keep your canopy to 3 feet you can get them up to 1000k. Also, wide reflectors will allow closer to 2 and a half feet. But 2.5-3 tons sounds about right for 10x 600's with a burner and a dehumidifier. But if you have 10x 1000k you'll need 4 tons with a dehumidifier and burner. Make sure your lights aren't closer than 5 feet from each other from the wide angles or you'll burn your plants. Vented will always be more trouble without a lot of foresight, because... bugs, condensation, mold spores, controlling your temp and humidity can be a challenge, especially during the hottest and coldest months. During hot months it's temp, in cold months it's humidity. Plus in a vented room your co2 will always cost you much more. 6x 1000W would be 3 tons.