I have a 72" T5 fixture over my 125g tank and love it. My tank is shallow enough (under 24" deep) to where T5s are adequate. I was happy that I could avoid Metal Halides because I don't care for the heat output and energy consumption of the MTs.
If I could do one thing different about the T5S though I would go with a fixture that takes shorter bulbs.
Mine sort of alternately stacks several 60" T5s (overlapping in the middle and alternatingly cover the remaining 12" on the ends).
60" bulbs are super tough to come by and since they are so thin tend to break in shipping. I had a tough time getting a replacement after one bulb arrived broken.
So if I had to do it over I'd get a fixture that takes 36" bulbs end to end.
You can always find those. With the 60" bulbs I am much more limited.

Have fun with the LEDs. Would be cool if it worked out.