I have been an advocate of T5's for some time now. I have never used metal halides over a reef tank, only reptiles, so I can't really comment on T5's vs. MH's. I get good growth, great colour rendition which I can tailor to suit my likes. Here are my tanks that are on T5's. I apologize, my quick editing has left the tanks looking dull, and they are much more vibrant in person.
85 gallon display:
Top
AquaScience Blue 22000
AquaScience Special 15000
KZ Fiji purple
AquaScience Special 15000
AquaScience Blue 22000
AquaScience Blue 22000
BOTTOM
Two 4" fans running air across the length of the bulbs.
Dawn/Dusk Bulbs
Dawn/Dusk Tank
Daytime Bulbs
Daytime Tank
40 gallon Frag Tank
TOP
KZ New Generation
AquaScience Blue 22000
KZ New Generation
AquaScience Blue 22000
BOTTOM
Open to air, no active cooling (I will add fans at some point, I'm just lazy right now)
Bulbs (I was running 2 Fiji Purple instead of the instead of the AquaScience Blue 22000 but I switch to get colour instead of growth)
Tank
10 Gal Canreef Contest Tank
AquaScience Blue 22000
AquaScience Blue 22000
Two 3" Fans drawing air out of the hood.
Bulbs (Notice the difference between the left and right bulb. The one on the left is 5 months old; the one on the right is brand new)
Tank
