Plants can stretch because of not enough light and too much heat. If you want nice dense nugs then you need to use more light and if you have a 400 mh than that's what you should start with if you don't have a few cool cfl's, and if you do have cfl's then just use them for about a week then move them to the mh. For the first week you need to gradually bring the MH closer and monitor the plants reaction this will provide better results over all. And when you are thinking about light spectrum, 3000k versus 6500k you aren't measuring it in a daily cycle, it is measured in a seasonal cycle, LOL. Rotations with the sun and earth and all of the technical stuff do actually make a difference in vegetation from country to country and coast to coast. Also typical warm, soft and cool generally all cost the same for the same wattage.
If you cant find the K on the package then look on the bulb. Bottom line, try to stay away from soft, don't understand why, then do a side by side grow and you will.
Adieu