Genetics will help determine how tall your plants will get, but how long you veg them, and whether you crop them or not, will also determine how tall they get.
Keep in mind that you might have to keep the metal halide up to 18" (400 watt lamp) away from the tops of your plants, so you should consider that when determining how tall you want your plants to be. It seems to me that with the only 43" from the floor to the light your plants will have to be short. If you subtract 18" (the distance of the light from the top of the plants) from 43", and then subtract about another 10" for the height of the pot that you're using, you have about 15". Yeah, your plants must be kept short. I don't know about White Widow, but I wouldn't let those veg for long. Wait, and someone else will join in and help out.