I am also in the process of a 60 Cube build. I love the ATI T5 fixtures , but miss the shimmer with them (colors and par are great). I have a 24" Ecoxotic Panarama Pro LED fixture with 9 modules, that will work, but in a 24" deep tank, I am not sure if I will get the penetration I need with the Pros.
In the end, I decided to hang one of my 250 Halides over the cube. I have a ballast that will overdrive the bulb 10%. That and a good reflector should be all the light I need. I have a batwing reflector now, but I am looking for a Lumenmax Elite reflector. I will prob throw 2-3 of the Panorama Pro modules on the 60 cube for dusk/dawn effect.
I will keep the Panorama Pro fixture with 6-9 modules over a 24x24x10 frag tank. I am having very good growth with the LED's so I will still use them on the frag tank, because its shallow, and rimless.
My 60 Cube has a hood to hide the halide, and help with light scatter.
You have a LOT of options with a 60 cube......choose wisely. I think a 250 Halide is perfect with a good bulb, like a Phoenix or Radium.
Herbie