You definitely need individual reflectors for T5s but it really doesn't matter in terms of T5 or MH. For example;
I was thinking of setting a up 75 gallon tank. I could do:
6 regular T5 bulbs= 324 watts
or
two 175watt MH=350 watts
the other option is
6 overdriven T5s=480watts
or
two 250watt MHs=500 watts
Same amount of watts either way. Also heat wise, fluorescent and MH are damn near identical. It's true, wives tales aside there is an RC thread with links to (can't remember the government agency as I'm doped up on allergy medicine). IIRC around 17% of the energy put into a MH bulb was given off as heat whereas 18% of energy put into a fluorescent bulb was given off as heat.