I think there are benefits and drawbacks for each setup (MH or T5). I am really liking the coloration and growth I am currently getting with T5s. IMO, the big 3 (lighting, water quality, flow) are hugely important, and T5s or MH suffice for the lighting portion, especially for SPS.
One of the big differences between T5 and MH is the light distribution pattern. There are fewer low-light areas with T5s unless you manufacture shade either with the rockwork, or by having decent sized corals above other things. I originally had difficulty finding good spots for corals that didn't like being blasted with light. IMO, the same issue happens with flow. As my tank has matured and things have grown, I have seen a huge transition. My cali tort is the best example. It took its time for about a year -- thickening up, but not really growing. It was purple with green polyps. Now it has neon blue growth tips, purple leading up to the growth tips, orange and gold more towards the center, and greenish polyps, though the ones towards the tip aren't so green. So the coral has taken on a really awesome rainbowish look -- I think in part due to tank aging, in part due to changing flow from growth elsewhere. I think this coloration would be there if I used halides as well -- though the coloration may be slightly different with diff wavelengths/intensities.
So my opinion is that coloration and growth are not only related to lighting, and some of the folks who "switch" may be blaming things on the lighting, when it really is a balance of a bunch of different factors. For example, I don't think I used to feed enough or have a big enough bioload to get enough food for the corals. I'm more happy than ever with my current setup. The only thing I am dissatisfied with at this point is the size of the tank
