I can tell you now that heat is a big problem with running that big of a light over that size tank. I have a 25g with 250 HQI and 2-28w actinics. I have a hood, so that doesn't help, but I had to put 2 4" fans with holes drilled along the back side of the hood for the air to flow over the water surface. With my apartment at 75, I couldn't keep the temp under 84 after about 4 or 5 hours of the halide on.

I had a 70w halide over a 10g and it grew stuff great. Also, I have a friend here that is growing a stag and a cap under the normal lights that come with the 12g aquapod. The 70w would be plenty and they are now coming out with more 70w bulbs in different colors since people are using them more and more often with nano tanks.