rharlow, I understand your confusion and I almost wish this thread could be removed from RC. I'm going to state my "opinions" here and anyone has a chance to disagree...
No offense to FastUno, but it seems like he had a bad experience with T5s because he was one of the first to really try them on a part "softy" tank didn't realize how much light they actually put out. He's been using all kinds of screening methods and going through hell trying to get his corals acclimated. Plus, he had weird green coralline growing on the back glass and blamed that on T5s. FastUno, like a lot of other people thought that you need the same number or more T5s than VHOs because of this misleading "wattage per gallon" rule. The fact is that these T5s but out some serious light and the wattage per gallon rule isn't applicable. I really think that these T5s have gotten a bad rap because of his tank ...others are having better experiences with them.
But now, there are several of us, that aren't having the same problems he did....but I've learned some from him and others here. Instead of 3", my 5 lamps are 8-9 inches off the tank surface (I have a 20" tall tank). I made sure I had 3 ballasts so I can run any number of lights in case I run into acclimation problems etc. So far, I haven't had the degree of problems that FastUno had. Yes, there are some softies like a green striped, one purple, and an orange ricordia that don't like to be in the direct T5 light, even on the sand bed..I put them partially in the shade instead. My yellow/green kenya tree didnt like being halfway up in the tank...he started to shrivel and now on the sandbed he's doing great. I put my frogspawn 12" from the surface and he loves the light. I put my orange and green digita instantly 8-10" from the surace and they are happy campers. No screen method or using books, etc.
Here's some random thoughts about T5s (fact, opinion, etc).
1) 4 lamps will have enough power for your tank (but none of mine are actinics). If you use a couple of actinics..you might need 6. Either way, I would make sure to have a couple to a few ballasts to work with the photoperiod just in case
2) Your tank will look different colorwise with T5s than others and you need to realize that before hand.
3) The big problem with T5s is to get the flouresce that you get with other lighting. I supplemented mine with a VHO, but you almost need 2 VHOs when the other 4 T5s are burning. There are seem to be some good T5 actinics out now...so maybe this issue will get better. I still keep comparing my tank colors to others...but am beginning to realize that being unique is not a bad thing.
4) I have no heat issues at all....with a 3" fan, my tank stays at 80-81 degrees.
5) I have green corralline on my rocks..but so do my other 2 friends and we ordered live rock together from the same place. So I cant blame green corraline on the T5s. I dont have corralline on the back glass. (not yet anyway).
6) My electricall usage right now is probabably the equivalent of 250W a day from my 48" long, 20" deep tank (taking photoperiods into consideration). With halides, it could be twice as much or more. My bulbs will last twice or more times as long as the halides.
Conclusion... I'm still on the fence here. I almost wish I would have went with halides so I could be like everyone else and my corals would have the colors that they do in other tanks. On the other hand, Im glad I didnt have to have a chiller, etc and my tank does have a unique look, but not enough flouresce as I want and some colors don't pop out like my friends tanks. I can't really comment about growth because my tank is so new. I wish I could have gone with halides..but when I think about buying a chiller, I'm back happy with my decision.
I'll let Grim and the others fill in what I left out here. Good luck and feel free to ask more questions.