I am planning to switch to fluorescents for veg, as well, so i'm, glad to see this topic.
I was using two 400 watt MH conversion systems in veg, and the damn things are stretching too much. I had
much bushier plants under fluoros, so I'm moving those two 400 watters to bloom, to add to the 400 and 600 that are already in there(5.5 x 6.5).
I'm not going to use T5's though, I'm going with T8's. They work great if you use the 6 bulb fixtures,(bulbs are nice and close together) much better than the 400 watt MH that I'm using now. I'm getting a little over 4,000 lumens per square foot, and they cover more area very evenly, with no hotspots or weak spots. I already have some of the T8's, or I would probably go with the T5's, but i just can't justify spending the money, when the T8's work great, and are more efficient, per watt. Oh yeah....also, the T8's are only a good option if you go with the 6-bulb fixtures, because the other fixtures have the bulbs spread out too far, and won't give you enough light intensity. Ha, I sound like a T8 salesman.
Seriously though, those T5's will work great, as long as you don't plant to veg much bigger than 16-18". I plant to keep mine 14" or less.
heres a pic or to so you know what im talking about.
