What made you choose 70w bulbs?
The cost of the bulbs, height problems if I went with higher wattage bulbs, the heat it puts out is a little over a 45w CFL but also I can get a 70w bulbs with in 6 to 9 inches might be able to get closer if I get my cool tube up and running. Also the electric place that I got it at I got around $10 to $20 package discount since I bought the 70w MH bulb , 70w HPS bulb, 70w MH ballast, 70w HPS ballast.
Also I can mis my 70w MH with a 35w HPS and another thing I can just buy lizard light fixtures because they are ceramic and a $20 to $30 fixture can handel up to a 150w bulb but I wanted to make sure I didn't run into heat problems.
Another thing is that I could run 1 5 gallon rubber mate DWC system under a single 70w HPS or MH light.