I would think that a good short strain AND LST would help you out alot. With that 100w HPS your going to want to use that light and have it cover as much of every part of the plant as possible. If you grown one single cola, it will be a bigger single like bud, BUT, if you grow out your branches, and bend to keep it low, you can make sure all parts are getting the light evenly, and your buds may not be one main cola, but you are more than likely to get a noticeably larger yield. So its a decison you have to make for what you want. I know large single cola's look fat and nice, BUT, I myself would choose 2 ounces of smaller buds than 1 ounce of a large cola. Now if you plan to grow as many as you can in a smaller space, then yeah, allowing them all to grow into one large cola would probably be best. If this is the way you choose, try harvesting the upper half and letting the lower half go a little longer for some better yield. Also, if your in a tight space, try using some reflectives like mylar...this will allow you to get more out of your HPS. Remember, HPS promotes stretching too, so you may want to consider bending and training branches, because the upper portion is going to get far more light than the lower half, especially once you reach 2 foot, and with a HPS, it won't take long. If you can afford it, add some CFL in there, 1 on all sides, or at the very least, 2 parallel to each other.