Typically the lower the kelvin rating (K) the better growth you get. For example: refugiums do better with 6,500k - 10,00k bulbs because the agale is photosynthetic and feeds off of the lower spectrum. When you start dropping the kelvin you will notice the hue getting more yellow, but as you raise the kelvin, the hue gets more blue. It all depends on your preference. Most people who run 10k halides supplement it with some sort of actinic pc or t5 since it is so yellow. On the flipside, a lot of people like using 20k bulbs because they get the best "pop" effect out of their corals. I personally think 20k bulbs by themselves are too dark. That's why I prefer a median like 14k. Its got the blue color and will help with growth.
Here is a Kelvin Scale for a better understanding
When it comes to mounting halides. When using large pendant reflectors, I like to keep them about 16 inches above the surface of the water. Again though, it is all preference. When I had reflectors at a foot or closer I noticed substanctial temperature spikes. I would also recommend going open top with any halide. Another thing to consider is that the halide is also capable of heating the entire room it is in...I use fans aimed at the surface of the water to help keep temperatures down. ONE more thing Bob, when adding corals to this new halide tank, start them at the bottom to get them use to the stronger light.