T5 lighting is all about the reflector. A highly polished parabolic reflector can put 90+% of the light output down into the tank. Without that you're no better off than a standard bulb (well there are degrees of reflection for lesser designs).
I believe actinic lighitng is 50k. It depends on what look you want in the tank. If you plan on having sps
corals you should go with a combination of bulbs including tru actinic (420nm). There are many different types of bulbs to choose from in T% other than just 10k, 12k, 14k, etc.
I had 10k 150w MH
with 96w PC
true actincs. I just switched to LED
and I'm set at 14k. It took a few days, but I like the look a lot better now. Slightly bluer than what I had.
So decide on what you want in the tank and the color you want to see. Take a look at some store displays and ask what bubls they have in their T5 fixtures.