We would need much more info to help you determine the best bulb selection for your display. What size tank, what kind of corals do you want to keep, what ballasts will you run, and what look are you going for with the water (crisp white or blue)? The answer to the first question you asked is no all bulbs are not the same. I really like Giessman and ATI bulbs. Yes is the answer to the second question there is a difference between 6500k and 11000k. K stands for the kelvin range and this is a measurment of the bulbs wave length. A 6500k bulb will provide more par (this is a unit of measurement for the lights ability to penetrate water or its strength/intensity) than a 11000k bulb. It is best if you are running only T5 lighting to run a mix of bulbs to give you the best look and help you accomplish what your desired results are. the higher the kelvin the more blue the bulb will make the water and then there are actinics. Actinics are a 460nm wave legth that help flouresce your corals colors. I hope this helps but really we would need more info.
