Too much power for a 12G?

[doch]

OK, so I recently picked up a 12 gallon JBJ nano cube... it came with a PC fixture which will need to be upgraded. Some of you may have seen my post requesting a HQI light for it... here's the thing: When I originally made the request, I was thinking the tank may have been a 6 Gallon, so I was thinking that a 150 or 70 would work. I now know that it is a 12 Gallon, and am wondering if 70W HQI will be enough (It will be primarily SPS), or should I go for the 150? I really don't want to cook the tank, so if I can get by with the 70, good. Any input greatly appreciated, thanks!