in a 60x60x120 i wouldn't go for an HID, as it's getting much too warm (even with a cooltube, which is basically running the extraction fan through a tube that the light sits in).. You'll already have difficulties to find a filter/fan combination that fits inside the 60x60, easily, then let alone pulling it through a cooltube.. (unless you mount the fan and filter outside the tent.
I also just ordered a 60x60 (but 160 high) to add to my setups, and got myself quantum board LEDs for it, as they can provide a more even illumination, with much less heat-generation and less power consumption.
When ordering in China the price can be quite good. For instance Kingbrite uses original Samsung LEDs and are good quality. That's what i'll get for not only the 60x60, but i will also upgrade another one of my boxes with one of their boards.