With the T5 platform you may run into some issues. The bulb efficiency is directly proportional to bulb temp. The optimum cold spot temperature of the bulb should be approx 45c. This is measured approx just past the metal ring (the point where mercury condensates in the discharge tube at the stamped end of the lamp). The temperature at the center of the bulbs in my fixtures runs approx 165f with a cold spot of 35-40c (using infrared thermometer)
Take this temp rise and multiply it times the 6 48" long bulbs and you begin to see the scope of the problem, you cant cool the bulbs yet you must isolate the plants from their heat
Now most T5 ballast may be remotely mounted up to 20' away... but compared to the temp rise of the bulbs this is a minor point.
What you might consider and what I have tried to mimic is a wind curtain, it is a technology that I have experience with from industry. It is simple and if properly designed very effective.
Here is a good primer on the subject